III. 

 RETROSPECT; 



OR, 



HOW THE STORY OF THE WORLD IMPRESSES US. 



Iv. THE ABYSS OK* CENTURIES. 



THE AGE OP THE WORLD. 



WE stand finally at the end of the world's long history. 

 From fire-mist to man we have flitted in thought, and have 

 taken some note of the grand events of each aeon. We pause 

 now, to indulge in reflections. How inexpressibly magnifi- 

 cent a career ! How inconceivably vast the stretches of space 

 and time which it spans! How many centuries must have 

 been swallowed up in the stately transformations of the origi- 

 nal nebula ! There are other nebulae in our modern universe, 

 and we gaze on them from year to year, and fail to note the 

 progress of any change. But they are changing before our 

 eyes ; and we are beginning to record some slight variations 

 from their first observed aspects. How long a time is re- 

 quired for one revolution of a mass of nebular vapor a hun- 

 dred billions of miles in diameter, who can calculate? Who 

 guess ? How long to reach the ring-making rate of rotation 

 how long to throw off a system of planets and condense 

 to a sun ? 



Yet there are some data for a calculation. I might even 

 lead you to understand what are the grounds of a mathemat- 

 ical estimate, but it would too much lengthen this Talk. Pro- 

 fessor Newcomb has calculated that the heat evolved by the 

 contraction of the matter of the sun from an infinite distance 

 would last only eighteen million years. He assumes the sun's 

 288 



