58 ILLINOIS STATE ACADEMY OF SCIENCE 



upon such a magnificent organization without being pre- 

 pared to grant that the time-scale required in its build- 

 ing is equally magnificent. The apparent motions of the 

 stars in a million years as seen from the earth is less 

 than the familiar terrestrial motions going on about us 

 in a single second, and on such a scale it would require 

 over two million billions of years to correspond to a 

 single life time of three score years and ten. Such an 

 analogy, of course, is useful only in so far as it is help- 

 ful in maintaining our sense of proportion. 



Although the geological evidences do not carry us as 

 far back into the past as do the dynamical ones, neverthe- 

 less they are extremely valuable in that they assure us 

 of the steadiness of the sun's light and heat throughout 

 the geological record. The dynamics of the stellar sys- 

 tems deals only with the distributions of the stellar ve- 

 locities under the action of gravitation, and it is quite im- 

 material in these studies whether the stars are hot or 

 cold. If the contraction of the stars were the only source 

 of stellar heat, in a few hundred millions of years the 

 stars would all be dark and relatively cold bodies, but the 

 distribution of the velocities would go on just the same. 

 Eventually, that is to say after the lapse of a certain num- 

 ber of millions of billions of years, a steady state of mo- 

 tion will have been practically attained Avhether the stars 

 continue to be incandescent or not, and so far as we can 

 see the galaxy has an almost indefinite future before it 

 after it has attained the steady state. But the evidences 

 of geology, so far as they go, indicate that the state of 

 incandescence is one of permanence, and this is confiraied 

 by the complete lack of evidence of the existence of a cold 

 and solid star. 



The energy of the sun's radiation is about 1.2x10" 

 ergs per year. The radiation of the faintest known star 

 is about one two hundredth of this, Avhile the energy of 

 such brilliant stars as Rigel and Canopus must be a 

 thousand or perhaps ten thousand times as great. How 

 can such prodigious energies be maintained throughout 

 the vast intervals of time which the dynamics of stellar 

 systems seems to indicate; and furthermore, what be- 



