158 Sir Robert Ball [May 16, 



WEEKLY EVENING MEETING, 



Friday, May 16, 1902. 



Sir Fkederick Bramwell, Bart. D.C.L. LL.D. F.B.S. M. Inst. C.E., 

 Vice-President, in the Chair. 



Sir Robert Ball, M.A. LL.D. D.Sc. F.R.S., 



Lowndean Professor of Astronomy and Geometry, Cambridge, 



and Director of the Cambridge Observatory. 



The Nebular Theory. 



I STAND here to-night with a grave task before me. I am called upon 

 to expound, so far as my powers will permit, an exceptionally great 

 subject. How puny do all other things appear in comparison witli 

 the great Nebular Theory ! Our personal affairs, the affairs of the 

 country, the affairs of the Empire — indeed all human affairs, past, 

 present and future — shrink to insignificance in comparison with what 

 is revealed in that mighty chapter from the book of Nature which we 

 hope to open. 



The grand transformations through which the solar system has 

 passed, and is even now at this very moment passing, cannot be seen 

 by us poor creatures of a day, they might perhaps be surveyed by 

 beings whose pulses counted centuries instead of seconds, by beings 

 whose minutes were longer than the duration of dynasties, by beings 

 to whom an hour was far longer than all human history. 



The Sun appears constant in size and constant in lustre during 

 the brief interval of human observation, but the Sun has not always 

 been the same, it did not always shine as it does now, nor will it 

 continue for ever to shine as it does at present. Our great luminary 

 is smaller at the end of each year than it was at the beginning, the 

 same is true through indefinitely great periods of time. In a retro- 

 spect we see the Sun ever larger and larger, there was a time uncounted 

 millions of years ago when the Sun had ten times the diameter that 

 it now possesses, there was a time when the materials which now 

 form the Sun were expanded into a volume of diameter greater than 

 tlie diameter of the Earth's orbit at the present moment. But even 

 when the Sun was millions of times as big as it is now it was not 

 heavier — there could not have been appreciably more material in it, 

 though that material was enormously rarefied. Thus our reasoning 

 makes us think of an epoch when the Sun was very different indeed 

 from the globe which we know so well. It had then no Earth to 

 cherish with warmth and gladden with light. Our globe was in 

 those days truly •' without form and void." At the time when the 



