152 Royal Society : — 



familiar to my mind, and such obvious deductions from what I 

 had established, that I did not deem them of sufficient novelty 

 to present them to oar own local scientific Society. 



1 believe that no one who has the advantage of acquaintance 

 with Prof. Thomson will for a moment doubt his eagerness to 

 give due credit to M. Mayer's just claims. But has justice 

 been done to Thomson himself, who has done far more than any 

 other individual towards the application, development, and pro- 

 mulgation of the dynamical theory of heat ? I fear not. 

 I am, Gentlemen, 



Yours very respectfully, 



James P. Joule 



XVIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 71.] 



May 26, 1864. — Major-General Sabine, President, in the Chair. 

 ri^HE following communication was read: — 

 Jl " On the Spectra of some of the Fixed Stars." By W. Huggins, 

 F.R.A.S., and William A. Miller, M.D., LL.D. 



After a few introductory remarks, the authors describe the appa- 

 ratus which they employ, and their general method of observing the 

 spectra of the fixed stars and planets. The spectroscope contrived 

 for these inquiries was attached to the eye end of a refracting tele- 

 scope of 10 feet focal length, with an 8-inch achromatic object-glass, 

 the whole mounted equatorially and carried by a clock-movement. 

 In the construction of the spectroscope, a plano-convex cylindrical 

 lens, of 14 inches focal length, was employed to convert the image 

 of the star into a narrow line of light, which was made to fall upon 

 a very fine slit, behind which was placed an achromatic collimating 

 lens. The dispersing portion of the arrangement consisted of two 

 dense flint-glass prisms; and the spectrum was viewed through a 

 small achromatic telescope with a magnifying power of between 5 and 

 6 diameters. Angular measures of the different parts of the spec- 

 trum were obtained by means of a micrometric screw, by which the 

 position of the small telescope w T as regulated. A reflecting prism 

 was placed over one half of the slit of the spectroscope, and by 

 means of a mirror, suitably adjusted, the spectra of comparison were 

 viewed simultaneously with the stellar spectra. This light was usually 

 obtained from the induction spark taken between electrodes of diffe- 

 rent metals. The dispersive power of the apparatus was sufficient to 

 enable the observer to see the line Ni of Kirchhoff between the two 

 solar lines D ; and the three constituents of the magnesium group 

 at h are divided still more evidently*. Minute details of the methods 

 adopted for testing the exact coincidence of the corresponding metallic 



* Each unit of the scale adopted was about equal to -j-Jg-g-th of the distance 

 between A and H in the solar spectrum. The measures on different occasions of 

 the same line rarelv differed bv one of these units, and were often identical. 



