572 THE POPULAR SCIENCE MONTHLY. 



held by many astronomers, was controverted by others who maintained 

 that the light, supposed to come from primitive fire-mist or nebulous 

 matter, was in reality emitted by extensive sidereal groups, or vast 

 universes too distant to show their individual stars. But, after some 

 time, the round and the oval forms of many of these faint objects were 

 looked upon as marks of a concentration around a centre, and the rare 

 matter seemed to be emerging from its original chaotic state. It was 

 thus that Kant, guided chiefly by the observations of Maupertuis, ob- 

 tained a basis for his nebular hypothesis, which he published in 1755, 

 and which, in essential features, differs little from that which has been 

 held during the present century.. Yet the subject excited little atten- 

 tion until many years afterward, when Sir William Herschel made his 

 extensive and careful observations on planetary nebula, and pronounced 

 them incipient solar systems, while he looked on irregular nebulosity 

 as indicative of the presence of distant collections of stars. 



As the doctrine founded on these observations was generalized by 

 Laplace and supported by him with additional evidence, it obtained for 

 a while much currency in astronomical circles ; but it was seriously 

 shaken in 1845, when many of the supposed embryonic systems of Her- 

 schel were resolved into stars by the powerful telescope of Lord Rosse. 

 Yet, after a decline for a few years, the nebular hypothesis was revived 

 on this side of the Atlantic by the announcement of Kirkwood's anal- 

 ogy ; and some time afterward it obtained more decided support from 

 the authority of Kirchhoff, as, on the discovery of spectrum analysis, it 

 seemed to furnish a good explanation of solar phenomena. When Hug- 

 gins obtained positive proof of the gaseous constitution of many of the 

 irresolvable nebulae, the tide of scientific opinion set more strongly in 

 favor of the views of Herschel and Laplace ; but it was soon checked 

 when it was found that all the true nebulous objects had a uniformity 

 of composition, and consisted entirely of hydrogen, nitrogen, and an 

 unknown gas. It seems impossible that the vast diversity of material 

 objects in future families of worlds could be afforded by the agency of 

 three elements, one of which is noted for its reluctance to take part in 

 chemical combinations. In addition to this difficulty, the periodical 

 and the permanent changes, detected in certain nebulous objects by 

 Hind and Holden, differ widely from a slow transition into a planetary 

 system ; and they are fatal to the idea that these cosmical clouds were 

 in past ages impassive to physical influences and departed little from 

 their primitive condition. But facts still more difficult of explanation, 

 in regard to these celestial objects, have been made known by the re- 

 cent observations on Nova Cygni ; and the apparent metamorphosis 

 which was witnessed, of a temporary star into a nebula, was so little 

 expected that theory seems much at fault ; and it is evident that many 

 of the views on this obscure department of astronomy must be either 

 considerably modified or entirely abandoned. 



According to the crude opinions prevailing during the infancy of 



