*Note by the Editors.—On the subject of Dr Williams's paper we have received several communications from different correspondents. To insert these would occupy much more of our pages than in our estimation would be proper; and all of them, we trust, will be satisfied with the general assurance, that, however desirable it may be to criticise or defend the speculations of Dr Williams, we cannot allow that this Journal is a suitable field for such exercise. One only of these papers, that from Dr Williams himself, partly in defence, partly in further explanation of his views, we admit for the present, chiefly because the original paper appeared in our pages, and because the author conceives himself entitled to advance, in defence of his opinions, certain experiments which seem calculated to that purpose. We must, however, say, that after this we can admit no further papers on the subject, since it appears to assume a controversial aspect; and it need to be no matter of astonishment, if we declare at the same time, our intention to give no opinion whatever on the merits of the question at issue, or the conclusiveness of the arguments adduced.