3O THOUGHTS ON NATURAL PHILOSOPHY. 



consistent scheme of stellar evolution, in suggesting 

 that individual stars and clusters of stars were 

 formed by the condensation of this nebula substance 

 by the power of gravitation. 



During the first half of the present century 

 scientific opinion entirely reverted to the earlier of 

 Herschel's views. Changes in the outlines of certain 

 nebulae, and the absence of structure in others of the 

 " planetary " class, both of which Herschel, thinking 

 that he had established by observation, had advanced 

 in support of his later views, failed to receive 

 confirmation in their examination by later astron- 

 omers. As with increased telescopic power many 

 objects classed as nebulae were one by one resolved 

 into collections of stars, the conviction became 

 increasingly strong, that, with sufficiently refined 

 means, all would ultimately succumb : and when at 

 length, in 1850, the Great Nebula of Orion was 

 thought, from its appearance in the gigantic tele- 

 scope of Lord Rosse, to show indications of breaking 

 into clouds of stars, the riddle of the nebulae appeared 

 to be approaching its last solution. As clusters of 

 stars the nebulae found ready place in the specula- 

 tions of many astronomers, whose minds, in conse- 

 quence of the perfection displayed in the relations 

 between the Sun and planets, had become powerfully 

 impressed with the conception of a system as an 

 essential unit in the construction of the universe. 

 The planets, with their attendant satellites, formed 

 systems, fair images of the grander Solar System, in 

 which they were included. Each star was regarded 

 as a sun, the centre of a planetary system of its own. 



