660 



SCIENG.E. 



[N. S. Vol. VII. No. 176» 



character, is impossible with the less brill- 

 iant stars. 



One of the principal problems of the as- 

 trophysicist is to determine the course of 

 celestial evolution. It has been found that 

 the spectra of stars are susceptible of classi- 

 fication in a few well defined tj'pes, which 

 seem to correspond with different periods 

 in stellar development. Starting from the 

 great cloud-like masses of the nebulse, it is 

 supposed that stars begin to form in regions 

 of condensation, and that the great masses 

 of gas and vapor continue to contract under 

 the action of gravitation, meanwhile radi- 

 ating heat into space. It is known from 

 theoretical investigations that such cooling 

 gaseous masses not only continue to grow 

 smaller ; they also rise in temperature with 

 the advance of time. Finally a certain 

 point in their career is reached when the 

 rise in temperature ceases, though the con- 

 traction of the mass is not arrested. The 

 balls of condensing vapors continue to cool, 

 losing more and more heat, and becoming 

 smaller and smaller in diameter. It is per- 

 haps at about this period in their history 

 that they pass through such a stage as is 

 now exemplified by the Sun, which has pre- 

 sumably cooled from the condition of a 

 white star like Sirius to that of a star of the 

 second or yellow class. The spectra of 

 such hot stars as Sirius contain little more 

 than dark and esceedingl}'- broad lines, 

 grouped in rythmical order and due to the 

 gas hydrogen. As these bodies continue to 

 cool the strong lines of hydrogen become 

 less prominent, and lines due to metallic 

 substances begin to appear. These become 

 more and more striking, until finally we 

 reach such a type of spectrum as that of 

 Procyon, which is intermediate in charac- 

 ter between the Sirian and the solar stars. 

 From this point on we find a continual ap- 

 proach to the solar type, until at last stars 

 are reached whose spectra agree line for 

 line with that of the San. After passing 



through the condition of the central body 

 of the solar system the yellow and orange 

 color of the stars becomes more pronounced^ 

 and subsequently a reddish tinge appears^ 

 until finally stars of a deep red color are 

 found, which seem to mark the last stage 

 of development before complete extinction 

 of light. Through a part of this line of 

 evolution it is easy to trace the changes in 

 stellar spectra, the solar lines still continu- 

 ing to be present, and superposed upon 

 them a remarkable series of flutings which 

 are characteristic of these reddish stars of 

 the third class. But between such _stars 

 and those of the class which Vogel has 

 designated as Illb there seems to be a 

 break in the evolutionary chain. 



Stars of Class Illb are of an orange or 

 red color, and with the telescope alone some 

 of them cannot be distinguished in appear- 

 ance from the more fully developed stars of 

 Class Ilia. But in the spectroscope they 

 are entirely different. All of these objects 

 are extremely faint, the two brightest of 

 them being hardly visible to the naked eye. 

 For this reason but little has been learned 

 of their spectra, although the spectra of 

 stars like Vega and Arcturus, which are 

 some scores of times more brilliant, have 

 been carefully investigated by both visual 

 and photographic means. According to 

 Duner and others, the spectrum of the star 

 known as 152 Schjellerup consists of certain 

 heavy, dark bands, which coincide closely 

 in position with bands given by compounds- 

 of carbon, and, in addition to these, a lumi- 

 nous zone in the orange portion of the spec- 

 trum. Three or four of the most intense 

 solar lines have also been detected in these 

 objects. But beyond this it is impossible to 

 go with the appliances used in the earlier 

 investigations, although it may well be that 

 photographic methods would have greatly 

 changed the character of the results ob- 

 tained. 



During the past winter a photograph- 



