On the spectra of isotopes

Abstract

In a previous investigation a comparison was made of a number of lines in the spectra of ordinary lead and of lead of radio-active origin. The wave­-lengths of seven lines in each case were measured from plates taken with a concave grating, and were found to be identical for the two varieties of lead within the limits of experimental error, which was about 0·03 A. A further examination was made in the case of the line λ = 4058 A., which is the brightest line in the spectrum, by measurement of the interference fringes obtained by means of a Fabry and Perot étalon , and it was concluded that any difference between the wave-lengths of this line in the two varieties of lead was less than 0·003 A., which was the mean error in these measurements. Aronberg has recently made a comparison of the wave-length of the line λ = 4058 A. in the spectrum of ordinary lead, and of lead obtained from Australian carnotite, and from measurements made on plates taken in the sixth order of a 10-inch Michelson grating, has found that the wave-length of this line in the spectrum of the lead of radio-active origin is less re­frangible than the line in the spectrum of ordinary lead by 0·0043 A.