20 president's address. 



accomplishment, when it can be achieved by legitimate inquiry, is a 

 source of the purest and most satisfying enjoyment that science can 

 give. "We feel that enjoyment each time we repeat an old and perhaps 

 hackneyed experiment. The result is known beforehand, but be it 

 only that we expect the colour of a chemical precipitate to be green 

 or yellow, be it only that we expect a spot of light to move to the right 

 or left, there is always a little tremor of excitement at the critical 

 moment and a satisfying feeling of pleasure when our expectation has 

 been realized. That pleasure is, I think, enhanced when the experi- 

 ment is not of our own making but takes place uncontrolled by human 

 power. In one of Heine's little verses he makes light of the tears of 

 a young lady who is moved by the setting sun. ' Be of good cheer,' 

 the poet consoles her, ' this is only the ordinary succession of events : 

 the sun sets in the evening and rises in the morning.' If Heine had 

 been a man of science, he would have known that the lady's tears 

 found a higher justification in the thought of the immutable and inexor- 

 able regularity of the sun's rising and setting than in the fugitive 

 colour impression of his descent below the horizon, and that her 

 emotions ought to be intensified rather than allayed by the thought of 

 his resurrection in the morning. There are in everybody's life a few 

 unforgettable moments which, at quite unexpected times, vividly rise 

 in his mind, and there are probably some in this Hall who have 

 experienced such moments at the beginning of a total eclipse of the 

 sun. They have probably travelled far, and gone through months of 

 preparation, for an event which only lasts a few minutes. The time 

 of first contact is approaching, in a few seconds the moon is about to 

 make its first incision in the solar disc, and now the observer's 

 thoughts come crowding together. What if there were a mistake in 

 t)ur calculations? What if we had chosen a spot a few miles too far 

 north or too far south ? What if the laws of gravitation were ever so 

 little at fault? — But now at the predicted time, at the very spot so 

 anxiously watched, the dark moon becomes visible, and' the feeling 

 of relief experienced concentrates into one tense instant all the grati- 

 tude we owe those who have given precision to the calculations of 

 celestial movements and handed us the key of prediction in a simple law 

 which can be written down in two lines. It is this simplicity of the law 

 of gravitation, and its accuracy, which some day may show limitations, 

 but has hitherto withstood all tests, that gives to Astronomy its pre- 

 eminence over all sciences. 



Indeed, if we classify the different sections into which science may 

 be divided, I think it may be said that their aim, in so far as it is not 

 purely utilitarian, is always either historic or prophetic; and to the 

 mathematician, history is only prophecy pursued in the negative direc- 



