PAST AND FUTURE OF A CONSTELLATION 293 



ciate these, we must choose terms which correspond with them. The 

 earth has but one measure of time that can be employed here, viz., its 

 great year, the precession of its equinoxes — a slow revolution of the 

 globe, which is completed in more than 25,000 years. A period like 

 t hat might serve as a basis of measurement in geology and in sidereal 

 astronomy. Taking, then, four of these periods— in round numbers 

 100,000 years — we ought, after that length of time, to have a sensible 

 difference in the aspect of the heavens ; and, in fact, on computation, 

 I find that in this interval— which in the history of the stars is but a 

 brief span — all the present constellations will be broken up. 



In Fig. 2 I give the geometrical results of my calculations as to the 

 proper movements of the stars in Ursa Major. Here is to be seen the 

 shape which that constellation will wear 100,000 years hence. There 

 is nothing like a wagon in this new figure. Alpha has moved down- 

 ward and ranged itself on the right of Beta, and both of these lie on 

 one line with Gamma, and even with Eta. Delta, Epsilon, and Zeta, 



Fig. 2. 



Uesa Majob 100,000 Years hence. 



are seen ranged on another line. If, in that distant epoch, the lan- 

 guages of terrestrial man shall still give to this constellation the title 

 of the Wain, no one will be able to understand why. In considering 

 what a mighty change it is destined to undergo in the future, the 

 question arises, How long has it worn the shape in which it is familiar 

 to us, and how did it look ages ago ? One hundred thousand years ago 

 there were, as yet, in all probability, no human beings on the earth, 

 and the antediluvian monsters were the only creatures that could then 

 view the starry sky. 



Still, some of the older planets — Mars, Jupiter, Saturn, Uranus, and 

 Neptune — were, no doubt, inhabited even then ; and, as the heavens 

 have the same appearance when viewed from them as from the earth, 

 the dwellers in those worlds saw Ursa Major as it appeared in those 

 days. All that we have to do, in order to find the position of each 

 of the seven stars 100,000 years ago, is to move them back from their 



