314 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



peared suddenly in Corona Borealis, in the Great Nebula in Andro- 

 meda, and in Auriga. 



Huggins was among the first to apply the spectroscope to the study 

 of comets. A dozen papers by him, on cometary spectra, make inter- 

 esting reading, for they record the gradual evolution of our knowl- 

 edge of physical conditions existing in comets up to the year 1882. 

 For example, speaking of observations of Winnecke's comet of 1868 

 made on the evening of June 22, he says : 



When a spectroscope furnished with two prisms of 60° was applied to the 

 telescope, the light of the comet was resolved into three very broad, bright 

 bands. * * * 



In the two more refrangible of these bands the light was brightest at the 

 less refrangible end, and gradually diminished toward the other limit of the 

 bands. This gradation of light was not uniform in the middle and brightest 

 band, which continued of nearly equal brilliancy for about one-third of its 

 breadth from the less refrangible end. This bajid appeared to be commenced 

 at its brightest side by a bright line. 



The least refrangible of the three bands did not exhibit a similar marked 

 gradation of brightness. This band, though of nearly uniform brilliancy 

 throughout, was perhaps brightest about the middle of its breadth. * * * 



The following day I carefully considered these observations of the comet 

 with the hope of a possible identification of its spectrum with that of some 

 terrestrial substance. The spectrum of the comet appeared to me to resemble 

 some of the forms of the spectrum of carbon which I had observed and care- 

 fully measured in 1S64. On comparing the spectrum of the comet with the 

 diagrams of these spectra of carbon, I was much interested to preceive that 

 the positions of the bands in the spectrum, as well as their general characters 

 and relative brightness, agreed exactly with the spectrum of carbon when the 

 spark is taken in olefiant gas. * * * 



It was with the spectrum of carbon, as thus obtained, that the spectrum of 

 the comet appeared to agree. It seemed, therefore, to be of much importance 

 that the spectrum of the spark in olefiant gas should be compared directly 

 in the spectroscope with the spectrum of the comet. The comparison of the 

 gas with the comet was made the same evening, June 23. * * * 



The brightest end of the middle band of the cometic spectrum was seen to 

 be coincident with the commencement of the corresponding band in the 

 spectrum of the spark. As this limit of the band was well defined in both 

 spectra, the coincidence could be satisfactorily observed up to the power of 

 the spectroscope; and may be considered to be determined within about the 

 distance which separates the components of the double line D. As the limits 

 of the other bands were less distinctly seen, the same amount of certainty of 

 exact coincidence could not be obtained. We considered these bands to agree 

 precisely in position with the bands corresponding to them in the spectrum of 

 the spark. 



The apparent identity of the spectrum of the comet with that of carbon 

 rests not only on the coincidence of position in the spectrum of the bands, 

 but also upon the very remarkable resemblance of the corresponding bands 

 in their general characters and in their relative brightness. This is very 

 noticeable in the middle band, where the gradation of brightness is not uni- 

 form. This band in both spectra remained of nearly equal brightness for the 

 same proportion of its length. 



