28 J. MORISON : ADDRESS 



a nebulous star, then a bright-line star, a helium star, a Sirian 

 star, then a solar star like our Sun, a red star whose materials 

 are cooler and denser, and finally a dark star whose matter has 

 become cold and solid. On a still larger scale we have one of 

 the great nebulae, then a nebula with luminous points in it, next 

 a nebula containing undoubted stars, and finally a star-cluster. 

 And we must remember that all these different forms shade off 

 gradually into each other. Add to this the fact that all these 

 bodies seem in the main to be composed of the same materials. 

 Can we doubt that the history of all these Ijodies is practically 

 similar, that every star has had a beginning, and in process of 

 time will have an end, and that the differences amongst the 

 celestial bodies are mostly due to their being at different stages 

 of their existence ? In the Solar System we have a number of 

 bodies all related together and j^resumably of much the same 

 age, though at different stages of their development ; while in 

 the Universe of Stars we have an immense multitude of bodies 

 apparently imconnected together, or belonging to different stellar 

 systems, not only at very different stages of existence, but almost 

 certainly of very different absolute ages. Some of these celestial 

 objects are, we may say, in nebulous infancy ; others are in their 

 prime, at the height of their gloiy and brilliancy ; while others, 

 again, are in a condition of stellar old age. It is worth noting 

 that all our Sun's immediate neighboui-s are, like him, in the 

 middle pei'iod of their existence, while the youngest and the very 

 oldest stars are all or nearly all in the Milky Way. The nebulae, 

 again, are scattered all over the heavens, though most numerous 

 in those parts far from the Milky Way, and are all at 

 incalculably remote distances from us. 



Two different hypotheses of the mode of development of the 

 Universe have been propounded. According to Laplace's Nebidar 

 Theory the Solar System was at some remote period a great nebula 

 extending far beyond the orbit of Neptune. This nebula rotated 

 on its axis. As the great mass cooled it contracted and became 

 more condensed in its central parts. As it contracted it rotated 

 more rapidly, and owing to the influence of centrifugal force the 

 outer part separated as a ring. The inner portion continuing to 

 contract, a second ring was formed in the same way. In this 

 manner the nebula finally separated into a series of rings, all 

 revolving in the same direction around each other and around 

 a central nebulous mass. The matter of each ring continued to 

 cool and condense, condensing in some parts more rapidly than 

 in others. The effect of this would be to draw into a single mass 



