SKETCH OF LEWIS MORRIS RUTHERFURD. 407 



mining the relative positions of thirty-one stars in the Pleiades. 

 On the same day Mr. Rutherfurd communicated orally to the 

 Academy a detailed account of his experiments, difficulties, and 

 successes, and of the methods which he had finally adopted. His 

 photographs of the moon are remarkable for the fineness of their 

 details. 



In 18G3 Mr. Rutherfurd published in the American Journal of 

 Science a paper dealing with the spectra of the stars, the moon, 

 and the planets, the first published work of the kind after that of 

 Bunsen and Kirchhoff, and the first attempt at classifying the 

 stars according to their spectra. In this paper he said : " The star 

 spectra present such varieties that it is difficult to point out any 

 mode of classification. For the present, I divide them into three 

 groups : first, those having many lines and bands, and mostly re- 

 sembling the sun, viz. — Capella, (3 Geminorum, a Orionis, etc. 

 These are all reddish or golden stars. The second group, of which 

 Sirius is the type, present spectra wholly unlike that of the sun, 

 and are white stars. The third group, comprising a Virginis, 

 Rigel, etc., are also white stars, but show no lines ; perhaps they 

 contain no mineral substance, or are incandescent without flame." 

 In 18G4 he presented to the National Academy of Sciences a pho- 

 tograph of the solar spectrum obtained by means of bisulphide-of- 

 carbon prisms, containing more than three times the number of 

 lines that had been laid down within similar limits on the chart 

 by Bunsen and Kirchhoff. In the course of his spectrum work, 

 to which he now gave increasing attention, he found, as he had 

 done in photographing, that the apparatus in use was insufficient 

 for his purposes. He noticed that diffraction gratings of finely 

 ruled lines upon glass and metal were preferable to series of prisms 

 for the decomposition of light in spectral study. The best gratings 

 in existence — still imperfect — were those of Nobert, who kept his 

 process a secret. Mr. Rutherfurd — as usual helping himself in 

 invention — devised a ruling engine capable of turning out much 

 finer gratings than those of Nobert, some of which had about sev- 

 enteen thousand lines to the square inch, and which have been 

 surpassed only by those since made by Prof. Rowland. With 

 these gratings his great photographs of the solar spectrum — more 

 than eleven feet long — were made. 



After he ceased to take an active part in astronomical work, 

 Mr. Rutherfurd gave his instruments and photographs to Colum- 

 bia College : the telescope in December, 1883 — and it is now 

 mounted in the observatory one hundred and ten feet above the 

 ground ; the machine for making measures in the same year ; and 

 his best negatives in November, 1890. This valuable collection of 

 photographs of the sun, the moon, and the star clusters has been 

 placed in a fire-proof vault. It contains, according to a list pub- 



