56 The Ottawa Naturalist. [June-July 



are due to collisions and that after the vapour has cooled down 

 they become nebulae ready to again develop into suns. 



We may be able to roughly compute the probabilitv of such 

 collisions maintaining the energy of the universe. We may 

 assume that the time required for a body to be developed from 

 the nebula, pass through all its stages to extinction, is of the 

 order of 500,000,000 years. If we further assume that there 

 are 100,000,000 stars in the visible universe it is evident that if 

 a new star and in consequence a nebula were to appear every 

 five years, it would suffice to maintain the universe at its 

 present brillancy. As a matter of fact, there seems to be no 

 doubt that, from the past few years, new stars have appeared 

 at intervals of from 5-10 years, which, allowing for the fact that 

 the less brillant of such objects may easily escape detection, 

 seems sufficient to establish a continuous cycle of development 

 of the universe. 



Hitherto we have considered the evolution of the stars or 

 suns themselves from the primal nebula, and have passed over, 

 what is fully as important from our standpoint, the formation 

 and development of planetary systems. Now that we have, 

 I hope, obtained some idea of the methods and laws governing 

 the formation of suns, we will have to consider those relating to 

 the attendants of the suns, the planets, and we will find that the 

 same principles apply. We know, of course, that our own sun 

 has a number of planets revolving around him, and travelling 

 with him in his journey through space but we have no means 

 of knowing except by analogy whether other stars are similarlv 

 accompanied for even the largest of telescopes could not possiblv 

 detect planets like ours. We do know that the double stars, 

 pairs of suns revolving around one another, can not have attend- 

 ant planets as the perturbations would soon cause them to be 

 drawn into one or other of the pair. The latest estimate places 

 the proportion of double stars as nearly one-third of the whole. 

 Of the remaining two-thirds, it seems probable that the condi- 

 tions, which gave rise to planets in our own system, should be 

 effective in many if not most of them, and there are likelv many 

 millions of planetary systems throughout the universe. 



The history of the development of planetary theories is a 

 most interesting one, but I have not time to more than brieflv 

 touch upon it. Although some vague and curious notions were 

 entertained by the ancients, it was not until the middle of the 

 eighteenth century that Wright of Durham, England, published 

 a theory of the universe. This was read by the young philos- 

 opher, Kant, who at once turned his brillant mind to the prob- 

 lems of cosmogony, and in 1755 published a treatise on the 

 subject, marked by the beauty and generality of its treatment, 



