Abstract
This article supplements the history of the pre-telescopic observations of the Moon at the turn of the seventeenth century with an analysis of the hitherto understudied manuscript Astrostereon or the Discourse of the Falling of the Planet (1603), written by Edward Gresham, an English astrologer and follower of the heliocentric theory. In this treatise, Gresham presents the results of his observations of the surface of the Moon. These findings are discussed against a wider background of contemporary writings by Galileo Galilei, William Gilbert, Johannes Kepler and Michael Maestlin. Furthermore, Gresham's studies of the Moon are shown as part of London astronomical pursuits represented by Gilbert, the author of the first map of the Moon made on the basis of naked-eye observations (c.1600), and by Thomas Harriot, who outran Galileo in telescopic observations of the Moon (1609). It is suggested that Gresham's reports may have helped Harriot to select the time of his first observation of the Moon and therefore determined its result.
Keywords: pre-telescopic observations of the Moon, Edward Gresham, Thomas Harriot, William Gilbert, Johannes Kepler, Galileo Galilei
Introduction
The way to systematic studies of the Moon's surface was paved by Galileo and his telescope. However, as argued by Stephen Pumfrey, an innovative observational programme aiming to elucidate the nature of the Moon had been formulated approximately ten years before Galileo, in the pre-telescopic age. These efforts originated with William Gilbert (1544?–1603), the queen's physician and author of the renowned treatise De magnete (1600).1 Gilbert introduced the said programme in his manuscript work entitled De mundo nostro sublunari philosophia nova (A new philosophy of our sublunary world). The text was also the first contribution to selenography, as it contained a map of the Moon.2 However, both De mundo and the map of the Moon were not printed until 1651,3 and historians of science first acknowledged the selenographic achievements of Gilbert only half a century ago.4
The second important contribution of London scholars to the early studies of the surface of the Moon were the first telescopic observations of the Moon made by Thomas Harriot (1560–1621) on 26 July 1609,5 four months before Galileo's observations. Unfortunately, Harriot's lunar observations remained unknown until 1785, when Franz Xaver von Zach mentioned them in the first published report about Harriot's extant astronomical notes.6 A more detailed account of these observations was offered half a century later by Stephen P. Rigaud.7 However, it was not until the 1960s and 1970s that these observations became part of the history of selenography, thanks to the analyses and publication of the lunar sketches made by Harriot.8
We know very little about personal relations which could have prompted the development of lunar studies in London at the turn of the seventeenth century. Pumfrey has recently argued that Gilbert's programme might have inspired Harriot at least partially.9 Accordingly, in his letter to Johannes Kepler of 13 July 1608, Harriot mentions the manuscript of De mundo left by Gilbert.10 However, this reference does not appear in the selenographic context and we cannot be sure if Harriot indeed saw Gilbert's Moon map.
Given the overall scarcity of evidence, each new source featuring an astronomer who observed the sky at the end of the Elizabethan period and/or the beginning of the Jacobean period and showed interest in the Moon and its nature seems immensely valuable. One such source is the hitherto understudied manuscript called Astrostereon or the Discourse of the Falling of the Planet. The treatise was written by Edward Gresham (1565–1613), and dated 1 September 1603 in the preface.11 The essay is rich in content and ideas, and it includes reports from the observations of the lunar disc made by Gresham, who clearly strives to draw his readers’ attention to his finding. While some fragments of the Astrostereon exemplify the opinions about the Moon which circulated among London scholars and practitioners at the beginning of the seventeenth century, Gresham was not a mere chronicler of his time. Set against a wider background of contemporary writings by Galileo, Gilbert, Kepler and Maestlin, who also tried to investigate the nature of the Moon's surface before the age of the telescope, Gresham's ideas appear truly original. Furthermore, it will be demonstrated in this article that there were sufficient similarities between the aims set by Gresham for observers of the Moon in 1603 and the first extant sketch of the Moon drawn by Harriot in 1609, to suggest that Harriot might have been aware of Gresham's account.
‘A very skilfull man in the mathematicks’
Very little is known about Gresham's personal life.12 He studied at Trinity College, Cambridge (BA 1584), where he probably earned his MA by 1606. In the years 1603–1607 he published astrological almanacs. Following the disclosure of the Gunpowder Plot, there were rumours that he had predicted these events in his 1605 almanac and he became implicated in the plot.13 Unfortunately, the said almanac is lost and we cannot assess the validity of these charges.
Interestingly enough, some critics believe that William Shakespeare's references to the disastrous consequences of the eclipses of the Sun and the Moon in King Lear (I.ii) were inspired by yet another publication by Gresham, namely a short pamphlet entitled Strange, fearful & true newes which hapned at Carlstadt, in the kingdome of Croatia, which he translated from High Dutch and edited.14 Gresham's preface is dated 11 February 1606 and indicates that he lived in the George house, next to Dyers Hall in Thames Street. The prophecy referring to unusual heavenly phenomena occupies less than four pages but it is preceded by a suggestive woodcut featuring the Sun and the Moon, a stylized comet, two armies in the clouds, and three enigmatic figures: a child with four heads, a black child and a child-death represented by a skeleton.
Gresham is also referred to in the comedy The Devil is an Ass (1616) by Ben Jonson:
Ay they do now name Bretnor, as before
They talked of Gresham, and of Doctor Forman,
Franklin, and Fiske, and Savory …15
Apart from Thomas Bretnor (1570/71–1618) all individuals mentioned by Jonson were involved in courtly intrigues, these being the divorce of Robert Devereux, third Earl of Essex from Frances Howard, and the poisoning of Sir Thomas Overbury.16 The report from the trial for Overbury's poisoning contains a very flattering assessment of Gresham's expertise: ‘without question he was a very skilfull man in the Mathematicks, and in his later time in witchcraft’.17
Gresham was certainly an adherent of the heliocentric theory. As noticed by Francis R. Johnson, he expressed this belief in his almanacs.18 For example, he is absolutely explicit about it in his almanac for 1606: ‘Our orb (as any other) obliquely circling the globouse body of light, is variablie affected with the light and darkenesse, and in uttmost limits with greatest difference.’19 However, the complete account of his astronomical beliefs can be found in his Astrostereon. In his almanac for 1607, Gresham himself advertises the extraordinary content of the Astrostereon:
And some (I heare) who (for that I am paradoxall in many things, but especially in the frame and systeme of the world, differing from all Phylosophers and Diuines in that poynt, as they thinke) absolutely condemne me of Atheisme and Haeresie. … if these … had ever seen my … Astrostereon (a book I wrote in the hart and heate of the last great Visitation, wherein with a reuerend reconciliation of the Word, with these scrupulous Paradoxes, I haue neither done iniury to God nor Nature) they would (without doubt) have been better opinionate of mee.20
In turn, in the catalogue compiled in Oxford in 1697, one of the extant copies of the Astrostereon was described in the following way:
Mr E. Gresham's Astrostereon, composed fourscore years since; wherein it is asserted, that the Planets are like the earth; that their influence is solely by Light and Heat; that the Sun is the Principle of Heat and Action; with many other particulars, which at that time were very rare.21
Some scant references to the Astrostereon in contemporary critical literature are hardly, if at all, more elaborate.22
To some extent, the fate of Gresham's Astrostereon resembles that of Gilbert's De mundo. The treatise remained in manuscript for a long time and ultimately never appeared in print as a whole text. Today there are five extant copies of the Astrostereon, of which only one is explicitly dated for 1610.23 However, there are no reasons to assume that it is Gresham's holograph. The other manuscripts were compiled probably between the 1640s and the end of the seventeenth century.24 In addition, the English astrologer John Gadbury (1627–1704) published fragments of the Astrostereon in his astrological almanacs for the years 1700, 1701, 1702, 1703 and 1705, appending the following note to the first imprint: ‘Something touching the Planetary Bodies, from the Learned Mr. Edw. Gresham, wrote near an 100 Years since, but never printed’.25 Gadbury published one third of the Astrostereon in the five successive almanacs, extensively editing the text. Significantly enough, Gadbury did not mention the title of Gresham's treatise in any of his almanacs, and he placed the extracts on the pages traditionally reserved for astrological commentary on planetary aspects, which is probably the reason why this partial publication passed unnoticed by later researchers.
The Moon in Gresham's universe
There are several topics addressed in the Astrostereon. First, the treatise contains a set of well-articulated arguments in favour of the heliocentric system and the new philosophy, and rejects the physics of solid celestial spheres. Secondly, Gresham argues that planets are made of the same matter as the Earth and therefore they are entirely opaque. Thirdly, he asserts that the Scriptures do not deny the possibility that the Earth moves as other planets do. Fourthly, the Astrostereon appears to be a remarkable example of an attempt to reorganize the fundamentals of astrology to fit into the new system of the universe and, finally, to employ them in a new type of prediction which would go beyond ‘vulgar astromancie’.26
The proximate reason for Gresham presenting his views on the structure of the universe (and the resulting significance of ‘true Phisiologie’) was an ominous prophecy circulating in London at that time. Based on the Book of Revelation, it associated the outbreak of the plague of 1603 with the prediction of the fall of a planet upon the Earth. According to Gresham, he and John Dee (1527–1608) were accused of authoring the prophecy.27 There were two catastrophic options foreseen: a planet could fall either upon the land or into the sea. Using astronomical arguments, Gresham argues that planets are bigger than the Earth (and all of them greater than the Moon) and therefore the predicted event was impossible.28 Any planet of this size would simply smash into both land and sea.29
However, Gresham goes beyond mere assessment of planetary diameters and discusses the very nature of planetary bodies. He strongly argues that planets are spherical, solid and opaque. To prove that planets are spherical, he relies simply on the sense of sight registering a round shape and even lighting. However, to prove that planets are solid and opaque, he presents more sophisticated observations. First he points to the well-known phenomenon of an eclipse of the Sun to demonstrate that the Moon is not transparent, and to the transits of Venus and Mercury across the Sun for the same purpose. Then he puts forward a novel argument which had not been invoked in the debates about Copernican or heliocentric astronomy before Gresham, namely the occultations of stars by planets. He starts with an account of his own observation of the occultation of a star in Virgo by Venus on 26 October 1601, and then he predicts twelve similar phenomena involving Venus, Mars, Jupiter and Saturn in the period from 29 September 1603 to 26 December 1604.30
The subsequent part of the discussion about the nature of planets is centred on the Moon. Gresham not only includes the Moon among other solid and non-transparent celestial bodies, but claims that the Moon is similar to the Earth because there are continents, oceans, capes, bays, islands, mountains, plains and hills on its surface.31 As in the case of the planets, Gresham reports his lunar observations.
To account for the difference in the brightness of large spots on the face of the Moon, Gresham points to the contrasting ability of land and water surfaces to reflect light. He believes that the brighter fragments of the Moon are covered with water, whereas the darker fragments denote land. He justifies his opinion by recourse to some simple observations of the appearance of objects on the Earth:
An argumente of which Phaenomene a Turfe[,] or clod of Earth[,] and a bason of water opposed to the beames shalbe sufficient[;] of which the one, (the water I meane) shall refracte such a glympse that the eyes cannot endure it, the other not so brighte yet such an one as in tyme dazelleth the eyes intentiuely behouldinge it[.] The like odds you may se[e] by bodies of glasse or pollished steele, or any other terse and pure bodie, in respecte of a grosse and opacous bodie if you obiecte them to the Sunns beames.32
In this way, Gresham adds his voice to a discussion dating back to antiquity and intensified at the beginning of the seventeenth century by scholars such as Kepler, Gilbert and Galileo. Commenting on Plutarch's dialogue Concerning the face which appears in the orb of the Moon (1st century CE), Kepler argued in his Optics (1604):
When Plutarch said that the moon is an earth, he then stated that the moon's spots are seas, which almost absorb the sun's rays transmitted into the deep, and do not reflect them as strongly as the earthlike parts usually do … Thus Plutarch, with whom I do not agree in this parts. It is more fitting that the bright parts that are in the moon be considered seas; those that are spotted, lands, continents, and islands.33
Interestingly, Kepler, like Gresham, justified his opinion by recourse to commonplace observation of reflecting surfaces. When he was in Styria in 1601 he observed a river from the top of Mount Schöckel (1446 m) and water appeared to him brighter, while landmass seemed darker.34 Gilbert interpreted the spots on the Moon approximately at the same time and in the same way as Kepler. On his chart of the Moon, he introduced thirteen topographical names, clearly associating dark spots with lands (figure 1).35 Needless to say, Kepler changed his opinion upon reading Galileo's Sidereus nuncius (1610), which he himself acknowledged in his immediately published letter to Galileo titled Conversation with the Sidereal Messenger (1610).36 Kepler's ultimate stance was responsible for the prevalence in selenographic literature of the firm dichotomy of mare to denote dark spots and terra to describe bright spots. Hence, in this particular case, Gresham shared the opinions of Gilbert and Kepler from the pre-telescopic age and likewise transposed the results of his observations made on the Earth onto the description of the lunar disc.
Figure 1.
Gilbert's map of the Moon as printed in his De mundo nostro sublunari philosophia nova physiologia (Amsterdam, 1651). (Courtesy of the Museum of Planetary Mapping.) (Online version in colour.)
Gresham also compared the shapes of the spots on the lunar disc with the shapes of earthly lands. This can be deduced from his ironic commentary on those who refused to watch the Moon carefully and instead satisfied themselves with the foolish tale about the Man in the Moon:
But such is the inveterate and self willed follye of men that I knowe the simplest and rudest of them will rather laughe at me for theis assertions, and attribute the Lunare apparances to a man with a bundle of thornes on his backe (a follye and bable never like heard of[)], then they will vouchesafe to lend one looke to correcte theire fopperye[.]
But if it be a man[,] I must tell them he had a soare legge[,] for the one is farre greater then the other, and he had a dogg too, (or els it is his bagge and bottle) before him[,] for there is a black spotte towardes the west lymbe of her as like a dogge as the other a man[.] I thincke if such ffooles weare as farre from the earth as the Moone is[,] they would saie the 2 pointe[s] of Land at Calecute and Mallaca shooteinge into the Ocean towardes the lyne were like the legges of a man, and the visible parte of the greate and maine contynent of Asia like his bodie and some burthen on his backe, for it is as like such a forme as that in the Moones Systeme very neare.37
Gresham's humorous parallels can be better understood if one examines the map of Asia (figure 2) in Abraham Ortelius's Theatrum orbis terrarium, a popular atlas frequently published during Gresham's lifetime (first edition 1570).
Figure 2.
Ortelius's map of Asia turned to the left. If we compare it with the right-hand half of Gilbert's map (figure 1), we have to agree with Gresham. Abraham Ortelius, Theatrum orbis terrarum (Antwerp, 1570). (Courtesy of Rare Book and Special Collections Division, The Library of Congress, Washington, DC.) (Online version in colour.)
On Ortelius's map Calecute is today's Kozhikode (or Calicut), a city in the south of the Indian subcontinent, on the Malabar Coast; the state (and city) of Mallaca (today's Malacca) can be found on his map in the southern region of the Malay Peninsula. It is the shapes of these lands that Gresham compares to two legs of clearly different thickness. A dog, in Gresham's view, would be either Sumatra (on Gilbert's map we can associate it with the nameless island closing Sinus Magnus), or Borneo (on Gilbert's chart an equivalent of Britannia, corresponding to Mare Crisium). To draw these parallels, Gresham did not even have to rely on the map of Asia from Ortelius's atlas. He could be perfectly satisfied with Ortelius's world map published in 1564, which was very popular in England at that time.38 Nor was the chart of the Moon necessary: it was enough to look at the lunar disc at an appropriate time. In fact we have no proof that Gresham ever saw Gilbert's chart or that he had a similar chart made by himself.
The naked eye and the uneven surface of the Moon
The description offered by Gresham goes beyond the well-known features of the lunar disc. He claims that he has noticed irregularities in the line of the terminator, which he takes for a range of mountains on the Moon similar to the earthly Pyrenees or Apennines. He encourages ‘those of little faith’ to make observations on their own when the Moon enters an appropriate phase between 29 September and 2 October 1603:
[F]urther[,] besides the like opacitie[,] impuritie of bodie[,] and like confirmitie of Earthly watrye superficialities, I haue discouered a gibbositie39 in one or twoe places of the Moone[,] especiallie from the mid-parte of her bodie Eastewardes; not unlike the great Pirenei Appenini or those huge and highe Mountaynes in Asia, dividinge that maine and vast continente from the uttermoste lymittes of the Tartarians frozen Ocean to the Indian Seas.
Of which apparance[,] if any man list to make further triall, lett him obserue the Moones bodie at tymes, conveniente from the 29 of this moneth of September to the 2 of October[,] and he shall perceaue an imparitye of illumination being a fuller of lighte in the middle, then for the proportion of her marginall Sun-shyne[.] [O]f which Phenomene who can assigne the realitie if not to be mountaines thwartinge the maine continente from the Easte to the west pointe of her, as God and nature hath ordayned this our Orbe[?]40
The cumulative evidence derived from Gresham's treatise alone shows that he was more than a random observer of the sky, and of the Moon in particular. If this is the case, what precisely could have caught his attention during his lunar observations and made him think that he had seen a massive mountain range? Gresham wrote that he had noticed ‘a gibbosity in one or two places of the Moon’ and reported that one of these features (which was easier to see and ran from the centre of the Moon's body eastwards) could be observed from the fourth day after the new moon till the first day after the first quarter. Unfortunately, today it is very difficult to determine what could be seen by a naked-eye observer of the Moon in the pre-telescopic age.41 The contemporary perception of the Moon is shaped not only by modern maps of the Moon and its photos, but by the overwhelming iconography of the space age. Additionally we have to account for the fact that, owing to the specificity of the Moon's movement, the appearance of the lunar disc, and therefore the description of its discernible features, depends to a large extent on the date when the observation is made.42
In the case of Gresham all we know is that he came to believe in the existence of a range of mountains on the Moon following his observations made before 1 September 1603. The fact that we do not know the dates of these observations, lack a sketch or drawing of any kind, and are left with the enigmatic nature of his account, makes it impossible to decide what seemed to him ‘a gibbosity in one or two places of the Moon’.
It is also possible that Gresham fell victim to his expectations about the surface of the Moon resembling our globe. Most certainly his belief in the ‘earthy’ nature of the Moon made him search the lunar disc for features which would confirm what he thought anyway, rather than look for ‘large or ancient spots’, to use Galileo's phrasing.43 But if that were the case, Gresham would not have been the only victim of such belief-driven observations.
The reports of Kepler appear to be one of the most interesting sources of information about pre-telescopic observations of the lunar disc in Gresham's time. Setting aside Plutarch's writings, Kepler was prompted to this type of research by Michael Maestlin (1550–1631), his tutor in Tübingen. Maestlin was a careful observer of the Moon and its eclipses.44 In his 1596 treatise entitled Disputatio de eclipsibus solis et lunae he offered an explanation of the grey light on the lunar disc.45 In 1605, while observing the eclipse of the Moon, Maestlin saw ‘a certain blackish spot … darker than all the rest of the body … You might have called the spot a cloud, which was spread over a wide area and laden with rain and stormy showers.’46 Maestlin observed with a camera obscura and believed that he had gathered observational proofs of the existence of air on the Moon.
Similarly, Kepler observed the Moon with a camera obscura, but he did so not only during eclipses. On 21/31 December 1602, he examined the distribution of light on the image of the lunar disc obtained shortly after the full moon. According to his report, he was able to discern ‘one continuous spot or darkness, darker in one place, lighter in another’.47 Finally, in his Optics, Kepler gave two arguments to prove that the surface of the Moon is strongly uneven:
First, it was said above that the moon, when it displays a bisected face, shows an uneven cutting, and to some extent a twisted one. This is evidence that some of its parts are low, others more raised up, and these to such an extent that it can be perceived from sixty semidiameters [of the Earth]. Next, in certain lunar eclipses there appears a great unevenness, and one not coming from the earth's shadow.
All these things provide me with evidence for my statement that the moon was correctly described by Plutarch as the kind of body that the earth is, uneven and mountainous, and that the mountains are even greater in proportion to its globe than are the terrestrial ones in their proportion.48
In a similar way Galileo, prompted by his naked-eye observations of the unevenness of the terminator, postulated the existence of mountains on the Moon. In his pamphlet entitled Considerations of Alimberto Mauri on some places in the discourse of Lodovico Delle Colombe about the star which appeared in 1604, published in 1606 under the pseudonym of Alimberto Mauri, Galileo argued (as if echoing Kepler):
it is not inconsistent to think that it is likewise not entirely even, but that there are also on the moon mountains of gigantic size, just as on earth; or rather, much greater, since they are [even] sensible to us. For from these, and from nothing else, there arises in the moon that scabby little darkness, because greatly curved mountains (as Perspectivists teach) cannot receive and reflect the light of the sun as does the rest of the moon, flat and smooth. And for proof of this I shall adduce an easy and pretty observation that can be made continually when she is in quadrature with respect to the sun; for then the semicircle is not smooth and clean, but always has a certain loss in the middle. For this, what more probable cause will ever be adduced than the curvature for those mountains? By that, and particularly in that place, she comes to lose her perfect rotundity.49
Consequently, Gresham's claims about the possibility of making naked-eye observations of the mountains on the Moon belong to a wider tendency gathering strength in European astronomy in the late pre-telescopic age. However, his remarks in the Astrostereon prove truly original, as they precede the opinions of both Kepler and Galileo, who published their treatises in the years 1604–1606. In view of the above, one cannot but wonder if these remarks, and in particular the passage reporting the existence of the range of mountains on the Moon, could be interpreted as evidence of the contemporary London quest to determine the nature of the Moon by observation. If so, did Gresham participate in the exchange of celestial novelties, or was he an outsider? And, last but not least, were his findings an inspiration for others, Harriot in particular?
The Moon of Gilbert, Gresham and Harriot
The opinions of Gilbert on the nature of the Moon and his map of the lunar disc were part of a wider programme to propose new physics and cosmology which was best described in his De mundo. In the passages of the Astrostereon devoted to the Moon, Gresham first and foremost endeavoured to convince his readers that the Moon is built like the Earth (and other planets). Referring to the spots on the lunar disc, he used arguments about water and land having different ability to reflect light. However, Gresham went even further and claimed that he saw a range of mountains next to the terminator when the Moon was approximately in the first phase. Moreover, he challenged ‘those of little faith’ to verify his observation, precisely indicating the age of the Moon which allows the mountains to be discerned.
In his extant writings, both printed and preserved in manuscript, Gresham does not refer to any earlier observations of the Moon. He could have been inspired by the previously mentioned selenographic inquiries of Gilbert, but we have no proof of such influence. If this was the case, Gresham would have to have known the results of Gilbert's studies directly from Gilbert, who died on 30 November 1603,50 and therefore after the Astrostereon had been written.
Our knowledge is even more limited about the beginnings of Harriot's lunar observations. We do not know why he directed his telescope at the Moon and for what purpose he made his first sketch (figure 3). Apart from the day and time of the observation, and the age of the Moon, the only information available is that the observation was made with the 6× telescope. The next extant observations were made in July, August and September 1610, i.e. after Harriot had read Galileo's Sidereus nuncius. These observations are accompanied by his first verbal comments, which show that by this time he had begun to describe the Moon in terms of geographical features.51
Figure 3.
Harriot's drawing of the Moon, 26 July/5 August 1609. (From Petworth House Archives HMC 241/IX f. 26. Courtesy of Lord Egremont and Leconfield.) (Online version in colour.)
Allan Chapman has suggested that, in the case of the first observation, Harriot wished to use the telescope to determine the exact time of quadrature, possibly as a means of determining the distance of the Moon from the Sun.52 Indeed, he did try to solve this problem but his earliest extant observation of this type comes from 11 January 1610/11, with the next from 9 April 1611.53 Harriot was appropriately equipped to make those observations (he had a clock or a watch), and apart from the sketches he left detailed notes with calculations. In both cases the Moon was precisely in the first phase, whereas on 26 July 1609 Harriot observed a five-day-old not a seven-day-old Moon.
As mentioned before, Stephen Pumfrey has suggested that Harriot's observations of the Moon could have been inspired by Gilbert's map.54 If so, Harriot would have aimed to compile the first telescopic map of the Moon to facilitate the study of, for example, the optical libration of the Moon. Such a map with features numbered and lettered has been found in Harriot's papers but we do not know when it was compiled, though it is usually assumed to have been the end of 1610 or the years 1611–1613.55 The diameter of this map is exactly the same as the diameter of the sketch of the Moon made on 26 July 1609 at approximately 6 inches, which may suggest the consistency of Harriot's observational programme.
The fragment of the Astrostereon where Gresham writes about the range of mountains on the Moon which he has discerned, and specifies the age of the Moon which allows his observation to be verified, invites yet another hypothesis concerning the origin of Harriot's sketch of 26 July 1609. Perhaps Gresham's remarks prompted the first telescopic observation of the Moon by Harriot, an observation which was not part of any comprehensive observational programme, which Harriot initiated only later. The hypothesis is supported by two facts associated with Gresham's description of the mountain range on the Moon. First, the date of Harriot's observation matches precisely the observational window recommended by Gresham as the best time to verify his report (from the fourth day after the new moon till the first day after the first quarter). Secondly, one of the most intriguing elements of Harriot's sketch appears to be the unevenness of the terminator clearly marked in the middle of the arch. The positioning of this feature corresponds to the area where Gresham identified a mountain range: ‘I haue discouered a gibbositie in one or twoe places of the Moone, especiallie from the mid-parte of her bodie Eastewardes’.
The technique of pen-and-ink drawing used by Harriot reveals which feature of the sketch required most intense study. While the terminator is represented with a diagonal dashed line, the centrally situated ‘gibbosity’ is marked with a continuous, thicker line, saturated with ink. The spots on the bright part of the lunar disc are drawn in a way similar to the terminator and they could be drawn on the basis of naked-eye observations. Considering the fact that the lines which denote the spots do not extend beyond the terminator, they must have been marked later than the terminator itself. This is yet another argument confirming the hypothesis that the central ‘gibbosity’ dominated the whole drawing process. Additionally, Harriot may also have devoted more attention to the right (lower) horn of the lunar crescent. He marked there a small feature, somewhat more conspicuous than the light shading of other spots drawn on the bright part of the disc. Apart from this small feature on the end of the crescent, one can venture to identify the formations on the surface of the Moon which Harriot tried to represent (figure 4). The lunar maria – Serenitatis, Crisium, Tranquillitatis, Fecunditatis and Nectaris – were charted by him with rather schematic shadows but in a relatively precise way.56 The intriguing protrusions in the middle of the terminator probably result from the observation of the three big craters located in close proximity on the edge of Mare Nectaris: Catharina, Cyrillus and Theopilus. This proves that Harriot was a good observer, particularly if one considers the pioneering nature of his observation. Consequently, one should assume that he found the graphically marked feature of the surface in the centre of the disc particularly important.
Figure 4.
The five-day-old Moon photographed on 15 June 2002. Comparing the photograph with Harriot's chart (figure 3), one can identify the lunar maria which he sketched: Serenitatis (1), Crisium (2), Tranquillitatis (3), Fecunditatis (4) and Nectaris (5). The arrow indicates the area which Harriot tried to depict by drawing some protrusions on the terminator. (Courtesy of John French.)
While trying to understand how Harriot made his first sketch of the Moon, one has to take into account a very important limitation. The field of view of his telescope probably did not cover the whole lunar disc. Unfortunately, the exact size of the field of view remains unknown and we can speculate about it exclusively on the basis of the results and descriptions of his observations. The problem was thoroughly examined by John North, who concluded that the field of view of the telescopes which Harriot used to observe the Moon ranged between 15 and 20 minutes of arc.57 Additionally, the clear field of view could be a bit smaller than the calculated or total field of view.
Our knowledge about the telescope used by Harriot to make the first observation of the Moon, a magnification of 6×, is particularly limited, as for his later observations he used instruments with higher magnification. If, following North's analysis, we safely assume that the clear field of view of this telescope approximated 15 minutes of arc, we can draw on Harriot's sketch of 26 July 1609 the circle with the diameter corresponding to this value (figure 5). This will help us to visualize how much of the lunar surface he was able to explore during his first observation.
Figure 5.
Above: Harriot's 26 July 1609 sketch of the Moon with the addition of a circle corresponding to a diameter of 15 minutes of arc, presumably the size of the clear field of view of the telescope used for the first observation. Below: The field of view of Harriot's telescope. The exercise underscores the fragmentary nature of the first images of the lunar surface. (Online version in colour.)
It is probably the limited field of view of Harriot's telescope that is responsible for misplacing the terminator on the 26 July 1609 sketch of the Moon.58 The terminator should have been drawn approximately 1/10 of the diameter higher than it is, and should have a slightly smaller curvature. At the same time, figure 5 makes us realize the size of the field of view occupied by the protrusions of the terminator, clearly marked by Harriot on the drawing. This is yet another argument proving that, while making his observation, Harriot focused specifically on this feature of the lunar surface.
The fact that Harriot's first telescopic observation looks as if it were an attempt to verify Gresham's report in the Astrostereon may be purely coincidental. We can even point to another probable source of Harriot's interest in the unevenness of the terminator: the already cited Optics of Kepler, with which Harriot was familiar.59 Unfortunately, currently there are no sources which would clearly demonstrate that the selenographic claims of Gresham were known in London, that they were verified by observations or that they were at least disputed. We know nothing about the possible connections of Gresham and his astronomical studies with Harriot. The only potential intermediary is John Dee, who kept in contact with Harriot,60 though we do not know whether Gresham's relationship with Dee went beyond the reference in the Astrostereon connecting their names with the ominous prophecy circulating in London in 1603.
Whatever the case, the fragments of the Astrostereon dealing with the observations of the Moon, and the historical circumstances which shaped Gresham's opinions, provide an interesting insight into the background to Harriot's work.
Conclusion
In ancient astronomy, the lunar spots were an important starting point for discussion about the similarities and differences of various heavenly bodies. The heliocentric theory of Copernicus further strengthened the concept of the Moon as a possible ‘second Earth’. At the turn of the seventeenth century, still in the pre-telescopic age, scholars tried to gather observational evidence which could help to determine to what extent the surface of the Moon might be similar to that of the Earth. The scholars who compiled their observational reports in the form of notes or charts were Michael Maestlin, Johannes Kepler and Galileo Galilei on the Continent, and William Gilbert in England. This list need to be supplemented by the English astrologer Edward Gresham, who not only vigorously propagated the idea of the existence on the Moon of continents, oceans, capes, bays, islands, mountains, plains and hills but also tried, as he claimed, to observe with the naked eye some mountain ranges on the Moon. He described these activities in his treatise Astrostereon or the Discourse of the Falling of the Planet which he dated 1 September 1603, a text that up until recently has neither been published in full nor carefully examined by historians of astronomy.
The naked-eye observations of the Moon described by Gresham (which are, by far, not the only original idea to be found in the Astrostereon) precede parallel publications by Kepler and Galileo from the years 1604–1606, and lie between the achievements of two other Englishmen: Gilbert, the author of the first map of the Moon (c.1600), and Harriot, the first observer of the Moon with the telescope (July/August 1609). Hence Gresham's treatise demonstrates that interest in the Moon in London was much wider than has previously been thought. Furthermore, the intriguing similarities between Gresham's claimed observation of the mountain range on the Moon and the first extant sketch of the Moon made by Harriot suggest that Gresham's findings may have inspired Harriot to make his first telescopic observation of the Moon at a time and in a manner suggested by the former.
Acknowledgements
I thank Richard L. Kremer for a discussion which helped to hone my arguments. This paper developed from research funded by the Polish National Science Centre within the framework of the grant no. DEC-2014/15/B/HS3/02490, titled ‘Tradition and novelty: Copernicanism, the idea of a plurality of worlds, and astrology in Edward Gresham's (1565–1613) Astrostereon’.
Footnotes
S. Pumfrey, ‘The Selenographia of William Gilbert: his pre-telescopic map of the Moon and his discovery of lunar libration’, J. Hist. Astron. 42, 1–11 (2011) (https://doi.org/10.1177/002182861104200205).
The term was also proposed by Gilbert in De mundo, and it proliferated in print thanks to Francis Bacon. See Pumfrey, op. cit. (note 1), p. 9, n. 3.
W. Gilbert, De mundo nostro sublunari philosophia nova (Amsterdam, 1651).
In 1965 Gilbert's De mundo was reprinted along with Sister Suzanne Kelly's companion volume, The De mundo of William Gilbert (Menno Hertzberger & Co., Amsterdam, 1965). See also S. Kelly, O.S.B., ‘The De Mundo Nostro Sublunari of William Gilbert’, Proc. Oklahoma Acad. Sci. 88–91 (1959).
5 August 1609 in the Gregorian calendar. The first systematic study of Harriot's lunar observations can be found in J. W. Shirley, ‘Thomas Harriot's lunar observations’, in Science and history: studies in honor of Edward Rosen (ed. E. Hilfstein et al.), pp. 283–308 (Ossolineum, Wrocław, 1978; Studia Copernicana 11).
See F. Xaver von Zach, ‘Anzeige von den in England aufgefunden Harriotschen Manuscripten’, in Astronomisches Jahrbuch für das Jahr 1788 (ed. J. E. Bode), pp. 152–156 (Berlin, 1785). However, von Zach mentions here the observations of the Moon without their dates. He focuses instead on the discussion of the observations of sunspots and Jupiter's satellites.
S. P. Rigaud, Supplement to Dr. Bradley's miscellaneous works: with an account of Harriot's astronomical papers (Oxford University Press, Oxford, 1833), pp. 20–21.
See E. Strout, ‘The very first maps and drawings of the Moon’, J. Br. Astron. Assoc. 75, 100–105 (1965); Z. Kopal, ‘The earliest maps of the Moon’, The Moon 1, 59–66 (1969) (https://doi.org/10.1007/BF00561770); O. Van de Vyver S.J., ‘Lunar maps of the XVIIth century’, Vatican Observatory Publ. 1, 69–83 (1971); Shirley, op. cit. (note 5).
S. Pumfrey, ‘Harriot's maps of the Moon: new interpretations’, Notes Rec. R. Soc. Lond. 63, 163–168 (2009) (https://doi.org/10.1098/rsnr.2008.0062).
J. Kepler, Gesammelte Werke, vol. 16 (C. H. Beck, Munich, 1954), p. 173.
Gresham works with the Julian calendar.
See Bernard Capp, ‘Gresham, Edward’, Oxford dictionary of national biography (Oxford University Press, Oxford, 2004).
Copies of Gresham's almanacs for those years, excepting only 1605, are extant. The following account can be found in the interrogation protocol of William Morton on 15 January 1604/5: ‘William Morton being first charged directly to have spoken very lately in conference with an acquaintance of his, that there would be fire and sword throughout all this land (one only place excepted) for religion amongst ourselves, answers that he never spake words importing any certain or known damage to this kingdom; yet he confesses that he has uttered (but knows not when or to whom) that he feared great troubles to happen within this kingdom this year, between Midsummer and Lammas, and that there would be fire and sword in divers parts. He thinks those troubles will be westward in the beginning and be stirred up by the Papists. For he has heard:— first, the prognostication of this year by Gresham in some places interlined in the book showed … ’ ‘Cecil Papers: January 1605, 16–31’, in Calendar of the Cecil Papers in Hatfield House: volume 17, 1605 (ed. M. S. Giuseppi), pp. 15–43 (His Majesty's Stationery Office, London, 1938), available online at British History Online, http://www.british-history.ac.uk/cal-cecil-papers/vol17/pp15-43 (accessed 19 September 2018).
See e.g. R. A. Fraser, Shakespeare poetics: in relation to King Lear (Routledge, London and New York, 2005; first published 1962), p. 21.
B. Jonson, The Devil is an Ass (ed. P. Happé) (Manchester University Press, Manchester and New York, 1996; first performed in 1616 and first published in 1631), p. 67.
F. R. Johnson, Astronomical thought in Renaissance England: a study of the English scientific writings from 1500 to 1645 (The Johns Hopkins Press, Baltimore, 1937), pp. 250–251.
F. Grevill, The Five Yeares of King James (London, 1643), p. 19. The text was probably written in the years 1625–1628: see N. Millstone, Manuscript circulation and the invention of politics in early Stuart England (Cambridge University Press, Cambridge, 2016), pp. 174–175, n. 22, which includes discussion about the book's authorship.
Johnson, op. cit. (note 16).
E. Gresham, A new Almanacke and Prognostication for the yere of our Lord God 1606 (London, 1606), f. B7v.
E. Gresham, A new Almanacke and Prognostication for the yere of our Lord God 1607 (London, 1606), f. B2v. See also J. L. Russell, ‘The Copernican system in Great Britain’, in Colloquia Copernicana I. Études sur l'audience de la théorie héliocentrique (ed. J. Dobrzycki), pp. 179–239 (Ossolineum, Wrocław, 1972; Studia Copernicana 5), at p. 213.
[E. Bernard], Catalogi librorum manuscriptorum Angliae et Hiberniae in unum collecti, 2 vols (Oxford, 1697), vol. 2, p. 221, entry 7131.
See K. Thomas, Religion and the decline of magic (Weidenfeld & Nicholson, London, 1971), p. 389, n. 22; B. Capp, Astrology and the popular press: English almanacs 1500–1800 (Faber & Faber, London, 1979), pp. 191 and 198; G. Parry, The arch-conjuror of England: John Dee (Yale University Press, New Haven and London, 2013), p. 265.
MS Sloane 753, 3279, and 3936, British Library, London; MS Ashmole 192 and 1807, Bodleian Library, Oxford. The only dated manuscript (1610) is MS Sloane 3936. There are important differences between the five extant copies of Astrostereon. All these differences will be discussed in detail in the upcoming critical edition.
These conclusions have been reached with the assistance of Dr Susan Davies, palaeographer from the University of Aberystwyth, who was immensely supportive in our early investigations.
J. Gadbury, EΦHMEPIΣ or A Diary (Astrological, Astronomical, Meteorological) for the Year of our Lord, 1700 (London, 1700), and for the following years. In the year of his death Gadbury did not publish any almanac for the year 1704, but he prepared for publication the almanac for the year 1705. He did not mention the title of Gresham's treatise in any of his editions.
This description features in the subtitle of Gresham's treatise: ‘Astrostereon Or A Discourse of the fallinge of the Planett Wherein by the true, though straunge[,] discovery of the Celestiall Orbs and manner of theire Action, upon inferior Subiects that Rumour with his Consequence is Subiected to the censure of the Simpleste: vulgar Astromancie, examined and true Phisiologie confirmed’. MS Sloane 3936, f. 3r, British Library, London. All citations are based on a semi-diplomatic transcription of excerpts from MS Sloane 3936. For the convenience of reading, in the transcribed passages raised letters have been lowered (e.g. ‘wch’ into ‘which’), all the contractions and special signs have been expanded, ‘thorn’ has been replaced by ‘th’ and terminal -es graph with ‘es’. Otherwise, the original variants of spelling have been retained. Some missing letters and words have been put in square brackets. Words which appear in the manuscript in italics have been italicized in the transcription. Original punctuation has been preserved, although at times it has had to be supplemented with modern conventions of sentence and clause division (shown in square brackets).
MS Sloane 3936, f. 4r–v, British Library, London. So far no other source referring to this prophecy has been identified. A brief reference to this affair can be found in Parry, op. cit. (note 22).
MS Sloane 3936, f. 18r, British Library, London.
To determine planetary sizes, Gresham relies on the system of planetary distances derived from Copernican astronomy, which he slightly modifies though he does not admit to it in an open manner: see MS Sloane 3936, f. 17v, British Library, London. Considering the fact that this problem raises a range of astronomical issues other than those discussed in this essay, a separate paper will be devoted to this aspect of his treatise.
Gresham does not reveal which astronomical tables he was using, but it has been established beyond any doubt that he worked with Copernican ephemerides (or tables): see J. Włodarczyk, R. L. Kremer and H. C. Hughes, ‘Edward Gresham, Copernican cosmology, and planetary occultations in pre-telescopic astronomy’, J. Hist. Astron. 49, 269–305 (2018), esp. at pp. 269–275 (https://doi.org/10.1177/0021828618790302).
MS Sloane 3936, f. 10v, British Library, London. According to Gresham, the Moon is inhabited. At this point, however, we are interested in the observational aspects of Gresham's treatise, and refrain from discussion of his philosophical interpretation of the nature of the Moon and the Selenites. Nevertheless, it is worth noticing that Gresham's stance has been entirely ignored in the relevant critical literature. For those interested, see the recent analysis in N. Fabbri, ‘Looking at an Earth-like Moon and living on a Moon-like Earth in Renaissance and early modern thought’, in Early modern philosophers and the Renaissance legacy (ed. C. Muratori and G. Paganini), pp. 135–151 (Springer Verlag, Cham, 2016).
MS Sloane 3936, f. 11v, British Library, London. Here and in all other citations the emphasis is added by Gresham.
J. Kepler, Optics: Paralipomena to Witelo & optical part of astronomy (trans. W. H. Donahue) (Green Lion Press, Santa Fe, NM, 2000), p. 262. In 1603, when Astrostereon was written, there was a new English translation of Plutarch's Moralia published in London, including a dialogue about the Moon. In this edition the passage referred to by Kepler (935 C) runs as follows: ‘like as this earth upon which we walke, hath many sinuosities and valleis, even so as probable it is, that the said heavenly earth, lieth open with great deep caves, and wide chinks or ruptures, and those containing either water or obscure air: to the bottome thereof the light of the Sunne is not able to pierce and reach, but there falleth, and sendeth to us hither a certeine divided reflexion’. Plutarch, The Philosophie, commonlie called the Morals, trans. P. Holland (London, 1603), pp. 1174–1175.
Kepler, op. cit. (note 33), p. 263.
See E. A. Whitaker, Mapping and naming the Moon: a history of lunar cartography and nomenclature (Cambridge University Press, Cambridge, 1999), pp. 13–15. The origin of this map is discussed by Pumfrey, op. cit. (note 1).
E. Rosen, Kepler's conversation with Galileo's Sidereal messenger (Johnson Reprint Co., New York and London, 1965), pp. 25–27. Galileo's arguments which convinced Kepler can be found in Galileo Galilei, Sidereus nuncius or The sidereal messenger (trans. A. Van Helden) (The University of Chicago Press, Chicago and London, 1989), pp. 43–44.
MS Sloane 3936, f. 12r–v, British Library, London.
See R. A. Skelton, introduction to facsimile edition of Ortelius, The Theatre of the Whole World. London 1606 (Theatrum Orbis Terrarum, Amsterdam, 1968).
The Historical thesaurus of English (http://historicalthesaurus.arts.gla.ac.uk) (accessed 5 June 2019) gives two basic meanings of this word: ‘curved surface’ and ‘protuberance/rounded projection’.
MS Sloane 3936, ff. 11v–12r, British Library, London. This fragment was edited and published by Gadbury, who deleted the dates of the observation recommended by Gresham and left only ‘at times convenient’: see J. Gadbury, EΦHMEPIΣ or A Diary (Astrological, Astronomical, Meteorological) for the Year of our Lord, 1701 (London, 1701), f. A7r.
We refrain here from discussing the possibility of the existence of ‘a Tudor telescope’ or astronomical applications of a proto-telescope in England long before Harriot. For relevant analysis, see A. Chapman, ‘Thomas Harriot: the first telescopic astronomer’, J. Br. Astron. Assoc. 118, 315–325 (2008), at pp. 323–324; S. Dupré, ‘William Burne's invention: projecting a telescope and optical speculation in Elizabethan England’, in The origins of the telescope (ed. A. Van Helden et al.), pp. 129–145 (KNAW Press, Amsterdam, 2010).
The attempts to date the first lunar observations of Galileo are a very good example of the significance of such conditions: see E. A. Whitaker, ‘Galileo's lunar observations and the dating of the composition of “Sidereus nuncius”’, J. Hist. Astron. 9, 155–169 (1978) (https://doi.org/10.1177/002182867800900301); O. Gingerich, ‘The curious case of the M-L Sidereus nuncius’, Galilaeana 6, 141–165 (2009).
Galileo, op. cit. (note 36), p. 40.
For an overview of Maestlin's observations and methods, see R. A. Jarell, The life and scientific work of the Tübingen astronomer Michael Maestlin, 1550–1631, PhD thesis, University of Toronto (1971), pp. 87–127; M. Schramm, ‘Zu den Beobachtungen von Mästlin’, in Zwischen Copernicus und Kepler. M. Michael Maestlinus Mathematicus Goeppingensis 1550–1631 (ed. G. Betsch and J. Hamel), pp. 64–71 (Verlag Harri Deutsch, Frankfurt am Main, 2002; Acta Historica Astronomiae 17).
M. Maestlin, Disputatio de eclipsibus Solis at Lunae (Tübingen, 1596), pp. 7–8. Kepler cites this passage in extenso in his Optics: English translation in Kepler, op. cit. (note 33), pp. 266–267.
Kepler cites Maestlin's description twice, in Dissertatio cum nuncio sidereo and Somnium; see Rosen, op. cit. (note 36), pp. 29–30; E. Rosen, Kepler's Somnium: The Dream, or posthumous work on lunar astronomy (University of Wisconsin Press, Madison, 1967), pp. 146–147. Maestlin's original is considered to be lost.
Kepler, op. cit. (note 33), p. 259. Kepler describes this instrument twice in his Optics (Chap. 2, Proposition 7 (pp. 67–69), and Chap. 11, Problem 1 (pp. 347–350)); he also offers a practical description of the use of a camera obscura during an eclipse of the Sun, with Maestlin participating: Chap. 11, Problem 7 (p. 362).
Kepler, op. cit. (note 33), pp. 260 and 262 (Chap. 6, Sect. 9).
Considerazioni d'Alimberti Mauri sopra alcuni luoghi del discorso di Lodovico delle Colombe intorno alla stella apparita 1604 (Florence, 1606), f. 15r. English translation in S. Drake, Galileo against the philosophers in his Dialogue of Cecco di Ronchitti (1605) and Considerations of Alimberto Mauri (1606) (Zeitlin and Ver Brugge, Los Angeles, 1976), pp. 104–105. For evidence concerning the identification of Alimberto Mauri as Galileo, see ibid., pp. 62–71; for objections to this identification, see W. H. Donahue, ‘Works ascribed to Galileo’, J. Hist. Astron. 10, 44–47 (1979) (https://doi.org/10.1177/002182867901000105). The authorship controversy is irrelevant for the construction of our argument. Far more central is the unquestionable date of its composition.
See S. Pumfrey, ‘Gilbert, William’, Oxford dictionary of national biography (Oxford University Press, Oxford, 2004).
Shirley, op. cit. (note 5), p. 303. The new charts show more features of the Moon's surface than his drawing from 1609 and appear more ‘Galilean’, which made some researchers think that they were made under the influence of Sidereus nuncius and it was only then that Harriot realized what he had actually seen while looking at the lunar surface with the telescope. See T. F. Bloom, ‘Borrowed perception: Harriot's maps of the Moon’, J. Hist. Astron. 9, 117–122 (1978) (https://doi.org/10.1177/002182867800900203). A similar assessment can be found in S. L. Montgomery, The Moon and the Western imagination (University of Arizona Press, Tucson, 1999), pp. 108–113; W. Shea, ‘Looking at the Moon as another Earth: terrestrial analogies and seventeenth-century telescopes’, in Metaphor and analogy in the sciences (ed. F. Hallyn), pp. 88–104 (Kluwer Academic Publishers, Dordrecht, 2000), at pp. 97–100. The form of the new charts has provoked a prolonged critical dispute that has also involved historians of art who have stipulated that Galileo's eye and imagination was fuelled by his intimate familiarity with a long artistic tradition of Florentine disegno, whereas Harriot lacked such aesthetic training. Compare, for example, S. Y. Edgerton Jr, ‘Galileo, Florentine “disegno”, and the “strange spottednesse” of the Moon’, Art J. (N.Y.) 44, 225–232 (1984); S. Y. Edgerton Jr, The heritage of Giotto's geometry: art and science on the eve of the SCIENTIFIC REVOLUTION (Cornell University Press, Ithaca and London, 1993), pp. 223–253; R. D. Huerta, Giants of Delft: Johannes Vermeer and the natural philosophers: the parallel search for knowledge during the age of discovery (Bucknell University Press and Associated University Presses, Lewisburg and London, 2003), pp. 54–57; M. Kemp, Seen / unseen: art, science, and intuition from Leonardo to the Hubble telescope (Oxford University Press, Oxford, 2006), pp. 44–47. Another interpretation of the problem which takes into account Harriot's cartographic interests was proposed by A. Alexander, ‘Lunar maps and coastal outlines: Thomas Hariot's mapping of the Moon’, Stud. Hist. Phil. Sci. 29, 345–368 (1998) (https://doi.org/10.1016/S0039-3681(98)00011-9). This opinion is shared by Pumfrey, op. cit. (note 9).
See A. Chapman, ‘A new perceived reality: Thomas Harriot's Moon maps’, A&G 50, 1.27–1.33 (2009), at p. 1.29 (https://doi.org/10.1111/j.1468-4004.2009.50127.x).
Shirley, op. cit. (note 5), at pp. 304–306.
Pumfrey, op. cit. (note 9).
Shirley, op. cit. (note 5), pp. 306–307; Pumfrey, op. cit. (note 9), p. 164; Whitaker, op. cit. (note 35), pp. 17–18; Chapman, op. cit. (note 52), p. 1.29.
Chapman, op. cit. (note 52), p. 1.29, postulates similar identification. However, Lacus Somniorum is indicated in place of Mare Serenitatis and Mare Nectaris is absent.
J. North, ‘Thomas Harriot and the first telescopic observations of sunspots’, in Thomas Harriot: Renaissance scientist (ed. J. W. Shirley), pp. 129–165 (Clarendon Press, Oxford, 1974), at pp. 144–150, 158–160. See also Shirley, op. cit. (note 5), p. 307.
This has been noted by Chapman, op. cit. (note 52), p. 1.28, figure 2.
That Harriot knew Kepler's work is demonstrated by letters written between October 1606 and September 1609. These letters were published in J. Kepler, Gesammelte Werke, vol. 15 (C. H. Beck, Munich, 1951), and vol. 16 (C. H. Beck, Munich, 1954). The correspondence has been analysed elsewhere, most recently in R. Goulding, ‘Chymicorum in morem: refraction, matter theory, and secrecy in the Harriot–Kepler correspondence’, in Thomas Harriot and his world: mathematics, exploration, and natural philosophy in early modern England (ed. R. Fox), pp. 27–51 (Ashgate, Burlington, 2012).
J. W. Shirley, Thomas Harriot: a biography (Clarendon Press, Oxford, 1983), pp. 80, 200–201.