September 9, 1915] 



NATURE 



41 



loi«s its'"^ effect by being placed before us in an un- 

 attractive form. This criticism also applies to Mach, 

 according to whom the object of science is to 

 economise thought, just as it is the object of a machine 

 to economise effort. Logically, this definition is 

 justified, and it may be the best that can be given, 

 if we prefer using a technical expression to confessing 

 an emotional feeling. But why should we do so? Is 

 it not better to recognise that human intelligence is 

 affected by sentiment as much as by reasoning? It 

 is a mistake for scientific men to dissociate themselves 

 from the rest of humanity, by placing their motives 

 on a different, and, at the best, only superficially 

 higher, level. When an adventurous spirit, for in- 

 stance, desires to organise an expedition to unknown 

 regions of the world, we try to induce our Govern- 

 ments to provide the necessary funds by persuading 

 them, and incidentally ourselves, that we do so because 

 important scientific results may be expected from the 

 expedition. This may actually be the case, but we 

 are mainly affected by the same motives as the rest 

 of the community; if the truth be told, we are as 

 curious as others to know what every corner of the 

 earth looks like, and we join them in wishing to 

 encourage an enterprise requiring perseverance and 

 involving danger. 



I fully realise that the wish to justify one's own 

 work in the eyes of the world will always lead to 

 fresh attempts to find a formula expressing the objects 

 which we desire to attain. Enough, however, has 

 been said to show that the definition must take account 

 of sentiment, without insisting too much upon it. Nor 

 can we hope, in view of the variety of intellectual and 

 emotional pleasures which combine to create the charm 

 of science, to include all points of view, but if I were 

 forced to make a choice I should say that the object 

 of science is to predict the future. The wish to know 

 what lies before us is one of the oldest and most 

 enduring desires of human nature ; often, no doubt, 

 it has degenerated and given rise to perverted and 

 ignoble longings, but its 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 tlie critical moment, and a 

 satisfying feeling of pleasure when our expectation 

 has been realised. That pleasure is, I think, enhanced 

 when the experiment is not of our own making, but 

 ikes place uncontrolled by human power. In one of 

 leine's little verses he makes light of the tears of 

 young lady who is moved by the setting sun. " Be 

 good cheer," the poet consoles her, " this is only 

 16 ordinary succession of events ; the sun sets in the 

 irening and rises, in the morning." If Heine had 

 »en a man of science, he would have known that 

 lady's tears found a higher justification in the 

 lought of the immutable and inexorable regularity of 

 le sun's rising and setting than in the fugitive 

 )lour impression of his descent below the horizon, 

 id that her emotions ought to be intensified rather 

 lan allayed by the thought of his resurrection in the 

 lorning — everybody's life contains a few unforgettable 

 joments which, at quite unexpected times, will vividly 

 rise in his mind, and there are probably some in this 

 hall who have experienced such moments at the begin- 

 ning of a total eclipse of the sun. They have probably 

 travelled far, and gone through months of prepara- 

 tion, for an event which only lasts a few minutes. 

 The time of first contact is approaching, in a few 



NO. 2393, VOL. 96] 



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 mis- 

 take in our 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 calcu- 

 lated spot on the sun's edge, the dark moon becomes 

 visible, and the feeling of relief experienced concen- 

 trates into one tense instant all the gratitude we owe 

 those who have given precision to the predictions of 

 celestial movements, leaving them expressible by 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 direction. It is no argument against my 

 definition of the objects of science, that a large section 

 of its subdivisions has been, and to some extent still 

 is, mainly occupied with the discovery and classifica- 

 tion of facts; because such classification can only be 

 a first step, preparing the way for a correlation into 

 which the element of time must enter, and which 

 therefore ultimately must depend either on history or 

 prophecy. 



Latterly men of science, and in particular physicists, 

 have given increased attention to the intrinsic mean- 

 ing of the concepts by means of which we express 

 the facts of nature. Everything — who can deny it? — 

 is ultimately reduced to sense impressions, and it has 

 therefore been asserted that science is the study of the 

 mind rather than of the outside world, the very exist- 

 ence of which may be denied. The physicist has thus 

 invaded the realm of philosophy and metaphysics, and 

 even claims that kingdom as his own. Two effects 

 of these efforts, a paralysing pessimism and an obscure 

 vagueness of expression, if not of thought, seriously 

 threatened a few years ago to retard the healthy pro- 

 gress of the study of nature. If the outside world 

 were only a dream, if we never could know what 

 really lies behind it, the incentive which has moved 

 those whose names stand out as landmarks in science 

 is destroyed, and it is replaced by what? By a 

 formula which only appeals to a few spirits entirely- 

 detached from the world in which they live. Meta- 

 physicians and physicists will continue to look upon 

 science from different points of view, and need not 

 resent mutual criticisms of each other's methods or 

 conclusions. For we must remember that most of the 

 good that is done in this world is done by meddling 

 with other people's affairs, and though the inter- 

 ference is always irritating and frequently futile, it 

 proves after all that our interests converge towards 

 a common centre. 



According to Poincar^, the pleasure which the study 

 of science confers consists in its power of uniting the 

 beautiful and the useful ; but it would be wrong to 

 adopt this formula as a definition of the object of 

 science, because it applies with equal force to all 

 human studies. I go further, and say that the com- 

 bination of the search for the beautiful with the 

 achievement of the useful is the common interest of 

 science and humanity. Some of us may tend more 

 in one direction, some in another, but there must 

 always remain a feeling of imperfection and only 

 partial satisfaction unless we can unit* the two funda- 

 mental desires of human nature. 



I have warned you at the beginning of this discourse 



