president's address — SECTION A. 81 



In a paper read before the Royal Society on December 18th, 

 1879, Dr. Huggins gives details of his work in photograpliing star 

 spectra since he began his new and successful process in 1876, 

 when he obtained seven lines in the photograph of the spectrum of 

 Vega. He used a prism of Iceland spar and lenses of quartz. With 

 this arrangement definition was so good that he could count seven 

 lines between H and K in the solar spectrum, and could photograph 

 star spectra from G to O in the viltra violet. He made it a practice 

 to set the slit always to the same width {^io of an inch), and he used 

 gelatine dry plates because they were more sensitive and could be 

 exposed as long as he desired. ^^ He had photographed the spectra of 

 Sirius, Vega, Arcturus, Beta Pegasi, Betelgeux, Capella, Alpha Her- 

 cules, Rigel, and Alpha Pegasi : also Jupiter, Venus, Mars, and por- 

 tions of the moon. The planetary spectra show no sensible modifi- 

 cation in the violet and ultra violet parts such as would result from 

 atmosphere on any of them. Six of the stars belonged to the " white" 

 cla.ss. In this paper Dr. Huggins states that the spectroscope aided 

 by photography miglit be made to afford valuable information in 

 the study of variable stars — a prophecy which we shall find was 

 fulfilled a few years later — and that it was evident the period of 

 the sun's rotaton could be determined by spectroscopic observa- 

 tions on each side of it. These brilliant results had not been 

 attained without a determined battle with the difficulties in instru- 

 ments and appliances then in use, and an amount of energy had to 

 be expended in that way that would have borne grand fruit had 

 instrument makers been equal to the demand of science. An 

 indication of what had to be gone through is found in the fact 

 that, in order to get the equatorial to follow the stars, it had been 

 necessary to get made no less" than seven different driving clocks. 



In July, 1881, Professor VogeP' announced his important work 

 and complete success in ])hotographing the specti-a of rarefied 

 hydrogen, which gave a spectrum almost exactly coinciding with 

 Dr. Huggins's ultra violet spectra of white stars. 



Dr. H. Draper^", on March llth, 1881, photographed the nebula 

 in Orion, and one of the stars shown in it is of 14*7 magnitude, 

 which is about the limit of what can be seen with a telescope of 

 that size. So he had just brought the star camera to record as 

 much as could be seen, and he would doubtless, had he lived a few 

 years more, have done what has since been done, viz., photograph 

 stars far beyond the range of vision : it was done soon after his 

 death by A. A. Comman and others. 



Between 1868 and 1881 improvement in spectra photographing 

 apparatus had been very great, but there had in the interval been 

 no comet bright enough to try the experiment of photographing 

 its spectrum, and Dr. Muggins^' eagerly seized the opportunity on 

 the 24th June, and succeeded in getting a fine photograjjh of the 

 spectrum of bright comet b of 1881. The photograph was the 

 result of an exposure of one hour, and on another bright night he 

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