PAPERS PRESENTED AT GENERAL SESSIONS 57 



encounters are fundamental events in the dynamics of 

 the galaxy for they alter radically the distribution of 

 the motions of the stars and bring about that particular 

 type of chaotic distribution of motions that is necessaiy 

 for a steady state. The studies of Charlier and Jeans 

 indicate that the steady state has not been attained in 

 the galaxy, for in the steady state we should not have 

 the phenomena of star clusters, star clouds nor star 

 streaming. But notwithstanding that the steady state 

 has not been fully attained, their conclusions are that 

 the galaxy is well advanced towards a steady state. It 

 is not necessary, of course, that two stars should ap- 

 proach as close to one another as the earth is to the sun 

 in order to affect their mutual motions, and more distant 

 encounters are much more numerous. But Jeans has 

 shown that it takes the more distant encounters forty 

 thousand millions of years to produce a cross velocity of 

 one kilometer per second, and he agrees with Charlier 

 that a cross velocity equal to the velocity of the stars 

 would require a million billion years. 



These results are not sufficient to enable us to compute 

 the age of the galaxy but they are sufficient to indicate 

 something of the order of magTiitude of its age. It can 

 hardly be less than thousands of billions of years and it 

 seems much more probable that it is of the order of 

 millions of billions of years. These figures are startling 

 and would doubtless leave us in a somewhat skeptical 

 frame of mind were it not for the fact that we have been 

 somewhat prepared for their reception by the equally 

 startling penetration of the astronomers into the depths 

 of space. It has long been a commonplace among them 

 that the galaxy is a physical unit so great that it takes 

 light from fifteen to thirty thousand years to measure 

 its diameter. Even though we bear in mind that light 

 travels three hundred thousand kilometers per second 

 and that there are over thirty-one and a half millions 

 of seconds in a year we appreciate but faintly the stu- 

 pendous scale upon which the galaxy is built — it is 

 roughly a billion times the size of the earth's annual 

 orbit about the sun. It is certain that we cannot reflect 



