30 J. MORISON : ADDRESS 



stars, and finally gets cold and becomes a dark star. The history 

 of a planet is much the same, only l)eing a smaller T)ody it parts 

 with its heat more quickly, and reaches the dark stage more 

 rapidly. In a great nebula such as the nebula in Orion, many 

 condensations would occur in different parts of the nebula, and 

 it would finally l)e converted into a star-cluster. 



I believe that the idea of meteorites in rapid motion constantly 

 coming into collision with each other and thus being partially 

 converted into incandescent gases originated with the late 

 Professor P. G. Tait of Edinburgh University, who suggested 

 this as an explanation of a comet's tail. He also held that 

 nel)ulae consist of clouds of stones in an atmosphere of hydrogen 

 which is rendered incandescent by continual collisions among 

 the meteorites. The late R. A. Proctor was also one of the first 

 to suggest the meteoric oi'igin of the Solar System. He says in 

 ' Other "Worlds than Ours,' published in 1870 : " Under the 

 continued rain of meteoric matter it may be said that the Earth, 

 Sun, and Planets are growing. Now the idea obviously suggests 

 itself that the whole growth of the Solar System from its primal 

 condition to its present state may have been due to processes 

 resembling those which we now see taking place within its 

 bounds." And again : " It seems to me that not only has this 

 general view of the mode in which our System has reached its 

 present state a greater support from what is now actually going 

 on than the Nebular Hypothesis of Laplace, but that it serves to 

 account in a far more satisfactory manner for the principal 

 peculiarities of the Solar System." 



The late Dr. Croll, in ' Stellar Evolution,' published in 1889, 

 elaborated what he called the " Impact Theory of Stellar 

 Evolution," originally proposed by him in 1868. According 

 to this our Sun and similar bodies were formed by the collision 

 of two dark stellar masses travelling through space at a speed of 

 at least 200 miles a second. Under the influence of gravitation 

 their speed became gradually accelerated as they approached 

 each other, till at the moment of impact they were rushing 

 together at the rate of at least 476 miles a second. Such 

 a collision instantaneously shivered them into fragments, and 

 the enormous quantity of incandescent gases generated at the 

 same time dispersed those fragments in all directions. By 

 constant collisions with each other the solid particles became 

 gradually converted into gases, and at length came to occupy 

 a space at least as large as the Solar System. This great mass 

 gradually contracted, and its subsequent history was that 



