48 



Dr. W. Huggins and Mrs. Huggins. 



[May 2, 



bunsen burner." At page 137 (Joe. dt.) Mr. Lockyer says : — " In the 

 nebulee we deal chiefly with lines seen in the spectrum of magnesium 

 at the lowest temperature." 



In a later paper in 1888* Mr. Lockyer states : — " In a paper com- 

 municated to the Royal Society on November 15th, 1887, I showed 

 that the nebulas are composed of sparse meteorites, the collisions of 

 which bring about a rise of temperature sufficient to render luminous 

 one of their chief constituents — magnesium. This conclusion was 

 arrived at from the facts that the chief nebular lines are coincident in 

 position with the fluting and lines visible in the bunsen burner when 

 magnesium is introduced, and that the fluting is far brighter at that 

 temperature than almost any other spectral line or fluting of any 

 element whatever." 



Although the number of direct comparisons which I had made 

 of the brightest line in the nebulas with N" T and with the lead line, not 

 to speak of the accordant results of the micrometric measures of 

 other observers, left great doubt in my mind whether this line could 

 be coincident with " the remnant of the magnesium fluting at 500," 

 really at 5006*5, yet I thought it desirable to undertake the laborious 

 task of comparing, with the necessary care and precautions, the 

 nebular line directly, in the spectroscope attached to the telescope, 

 with the spectrum of burning magnesium. 



Arrangements were made by which the light from burning 

 magnesium was thrown into the telescope from the side and then 

 reflected down, under conditions similar with the light from the 

 nebula, upon the slit of the spectroscope. By this arrangement any 

 flexure in the tube connecting the spectroscope with the telescope 

 would affect both spectra alike. The coincidence in position of 

 the spectrum from burning magnesium with that of a heavenly 

 body to which the telescope was so directed that its light fell upon 

 the slit of the spectroscope, was tested with great care on several 

 occasions by comparing the three bright lines of magnesium with the 

 corresponding lines, b 1? b%, & 4 , in the spectrum of the moon. Indeed, 

 to prevent any possible error in the observation of apparent want of 

 coincidence of the nebular line, if the light from the burning 

 magnesium should by an accident so come upon the slit as to bring 

 its spectrum in a very minute degree on the less refrangible side of 

 its true position relatively to the nebular line to be observed with it, 

 the arrangement was purposely made that the lines of magnesium 

 were seen to fall upon the corresponding dark lines at b in the moon, 

 a very little on the more refrangible side of the middle of those lines. 

 This state of things would diminish a little the interval which 

 should be seen between the nebular line and the edge of the 



* " Suggestions on the Classification of the various Species of Heavenly Bodies." 

 * Koy. Soc. Proc.,' vol. 44, p. 21. 



