254 ANNUAL OF SCIENTIFIC DISCOVERY. 



it appears small in quantity, is in reality quite remarkable, and bears 

 testimony in a high degree to their devotion and patience as, in con- 

 sequence of the few fine nights available when a star is in a good 

 position, the mapping of spectrum of a single star completely would 

 occupy several years. 



In the spectra of all the brighter stars that have been examined, the 

 dark lines appear to be as numerous and as fine as in the solar spec- 

 trum. No stars sufficiently bright to be observed are without lines, 

 and therefore star differs from star only in the arrangement of the 

 lines, and consequently in the elementary substances present ; but all 

 the stars arc constructed on one and the same plan. The number of 

 fixed stars observed by Messrs. Huggins and Miller, amounts to nearly 

 50 ; but the spectrum lines of only a few have been mapped with 

 any degree of completeness. . Among these are Aldebaran, and the 

 bright star designated as a in the constellation of Orion. 



Aldebaran is a star of a pale-red tint, and its spectrum is full of 

 lines in the orange, green, and blue. We shall presently see the signif- 

 icance of this fact. About 70 lines were tested as regards their coinci- 

 dences with metallic spectra, by direct comparison. Sixteen terrestrial 

 elements were thus made to present their characteristic bright lines 

 above the dark ones of the star ; and sodium, magnesium, hydrogen, 

 calcium, iron, bismuth, tellurium, antimony, and mercury, answered 

 perfectly to the test, and proved their existence in the atmosphere of 

 Aldebaran. Seven elements, nitrogen, cobalt, tin, lead, cadmium, 

 lithium, and barium, gave negative evidence only. Indications of other 

 elements were not wanting, but the observations of these fine lines 

 were too fatiguing to the eye to be pressed further. 



a Orionis has a very full spectrum. The light of the star is orange, 

 and the lines are thickest in the red, green, and blue. About 80 

 lines have been measured and mapped, and 16 elementary substances 

 tested for coincidence. With five of these, sodium magnesium, 

 calcium, iron, and bismuth, the connection is complete and cer- 

 tain. Perhaps thallium also exists, but the line seen might be cal- 

 cium, the apparatus not having dispersive power enough to separate 

 the lines of the two metals at that particular point. In the case of 

 hydrogen, nitrogen, gold, cadmium, silver, mercury, barium, and lith- 

 ium, coincidence was not proved. The absence of hydrogen in the spec- 

 trum of this star and some others is a point of considerable impor- 

 tance, as its presence is eminently characteristic of the spectra of the 

 sun and some 40 fixed stars, which have been examined. This 

 observation is, moreover, especially valuable, since it proves that the 

 lines which indicate its presence belong to the atmospheres of the 

 luminous bodies themselves, and not, as might have been expected, 

 to our own atmosphere. 



Although a very bright star, the observations of Sirius are exti*emely 

 difficult, from its low altitude in this latitude, by which it is brought 

 within the densest and most impure part of the atmosphere. Sodium, 

 magnesium, hydrogen, and probably iron, have been found by coinci- 

 dences, and a photograph of the spectrum was obtained on wet collo- 

 dion, but owing to the combined difficulties of the experiment, the 

 lines could not be traced in the picture. It is, however, believed by the 

 observers that further experiments will result in this important object 



