Figure 5. Fringes of equal chromatic order with iron reference spectra (positive print).

1. Aluminum films, reflection fringes, 10-μ spacer;
2. aluminum films, transmission fringes, 10-μ spacer;
3. 15 layer broadband films, transmission fringes, 17-μ spacer.

In c, the only obvious indication of the large dispersion of phase shift is the fact that the fringe spacing does not decrease monotonically with increasing wavelength. In the red the last few fringes are more widely spaced than those immediately preceding. Where several fringes are overexposed in the red the standard deviation in determination of wavelengths is about 0.4 A, whereas in other portions of the spectrum it is from 0.1 to 0.3 A.