SIR WILLIAM HUGGINS, K.C.B., O.M. 189 



and approach of the stars. Basing his method of attack on the 

 correctness of Doppler's principle, on the theoretical aspect of 

 which he received assistance from Clerk Maxwell, he sought for 

 signs of failure in exact coincidence between the absorption lines 

 in stellar spectra and the corresponding bright lines in terres- 

 trial spectra. By the principle, there must necessarily be a 

 change in the frequency of waves of light as perceived by an 

 observer on the earth if they emanate from a star which is in 

 motion, of approach or recession relatively to the earth. Such 

 a change would declare itself in the spectrum of a star by a 

 minute shift of the absorption lines towards the blue or the red, 

 according as the star approaches the earth or recedes from it. 

 After several years' work Huggins was able to assure himself of 

 the existence of such minute shifts and succeeded in measuring 

 them in the case of several stars. The practical difficulties of 

 applying the method were very great ; after Huggins and the 

 observers !at Greenwich and Potsdam and Rugby had done 

 all that was possible in the refinement of visual observations, 

 the work reached its limit for that time. Twenty years after 

 the publication of Huggins's memoir, and closely following his 

 success in photographing stellar spectra, Vogel made a great 

 advance in this department by introducing photographic methods 

 and after three years' work was able to publish the results of 

 his labour in the shape of the velocities of fifty-one of the 

 brightest stars visible at Potsdam. Since that time the work 

 has been carried on by many observers in various countries 

 and it is not too much to say that many of the most remarkable 

 advances recently made in astronomical knowledge are the results 

 of the development of Huggins's method. 



There are many other points that should be referred to in 

 a notice of Sir William Huggins's work. His investigations on 

 the spectra of the Wolf Rayet stars, his success in photograph- 

 ing the ultra-violet regions of the spectrum of the great nebula 

 in Orion, his studies of the spectroscopic phenomena of comets, 

 his development of the method of seeing prominences at the 

 limb of the uneclipsed sun, his analysis of the luminosity 

 produced by radium and its connection with the surrounding 

 nitrogen, are instances of an activity that was always at work in 

 the forefront of scientific advance. 



Many were the marks of distinction that were offered to Sir 

 William Huggins in recognition of his scientific achievements 



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