214 ASTROXOMY. 



accomplished. Several small stars were showu ou the uegative, sliiuiug 

 through the tail, though their light passed through probably 100,000 

 miles of cometic matter. This shows the exceeding transparency of 

 these bodies. 



Comet B, 1881.— An important note on the photographic spectrum of 

 comet 1>, 1S81, has been sent to the Koyal Society, London, by Dr. 

 Huggins. After subjecting the plate to an exposure of one hour with 

 the nucleus of the comet acting through one-half of the slit of the 

 apparatus (see for process "Philosophical Transactions of 1880," page 

 769), the open half was closed, the shutter withdrawn from the other 

 half and the instrument then directed to Arcturus for 15 minutes. The 

 result was a very distinct spectrum of the comet, together with the 

 spectrum of the star. The spectrum of the comet consists of a pair of 

 bright lines in the ultra-violet region and a continuous spectrum which 

 can be traced from about F to some distance beyond H. The obvious 

 inference he makes from the position and measurement, in wave lengths, 

 of the lines is that part of the light of comets emanates from them- 

 selves, and that part of their light is simply reflected sunlight. Further, 

 the spectrum would go to prove the presence of carbon in the substance 

 of comets, possibly in combination with hydrogen. Another photo- 

 graph was taken on June 25, when the plate was exposed for an hour 

 and a half, but it was so faint that the Fraunhofer lines could not be 

 seen in the continuous spectrum, although they were clearly observ- 

 able in the former photograi)h. But the two bright lines were very 

 distinct. Subsequently, on July 9, he found the wave lengths of the 

 two bright lines to be 3,883 and 3,870, and discovered that the less re- 

 frangible threw a Mnt luminosity beyond the second line. He saw. 

 too, the groups of lines between G and h usually associated with the 

 carbon compounds. His wave length for the less refrangible end of 

 the spectrum is 4,230. Nitrogen would seem, also, to be present in the 

 comet, besides carbon and hydrogen. Dr. Huggins concludes: •' It is 

 of importance to mention the strong intensity in the photograph of the 

 lines 3,883 and 3,870, as compared with the continuous spectrum, and 

 the faiut, bright group beginning at 4,230. At this part of the spectrum, 

 therefore, the light emitted by the cometary matter exceeded by many 

 times the reflected solar light. 



This bright comet was also successfully photographed by Dr. Henry 

 Draper in New York. The tail is 8° long on the picture, the exposure of 

 the negative plate having been three hours. Spectroscopic observa- 

 tions of the nucleus showed a continuous spectrum, with no absori)tion 

 lines (due to the coma) visible. The tail^ also, gave a continuous spec- 

 trum without lines. The coma gave a banded spectrum, showing it to 

 be gaseous. 



This object has yielded unparalleled opportunity for research on tli*: 

 physical constitution of comets. It has been abundantly photographed 

 by Draper and Common, and a series of drawings has been made by 



