20 



NATURE 



[September 2, 1920 



that speculation is premature. The time when specu- 

 lative theory and observational research may prohiably 

 go hand in hand is when the possibilities, or at any 

 rate the probabilities, can be narrowed down by 

 experiment, and the theory can indicate the tests by 

 which the remaining wrong paths may be blocked up 

 one by one. 



The mathematical physicist is in a position of pecu- 

 liar difiiculty. He may work out the behaviour of an 

 ideal model of material with specifically defined pro- 

 perties, obeying mathematically exact laws, and so 

 far his work is unimpeachable. It is no more specu- 

 lative than the binomial theorem. But when he 

 claims a serious interest for his toy, when he suggests 

 that his model is like something going on in Nature, 

 he inevitably begins to speculate. Is the actual bcdy 

 reallv like the ideal model? May not other unknown 

 conditions intervene ? He cannot be sure, but he 

 cannot suppress the comparison ; for it is by looking 

 continually to Nature that he is guided in his choice 

 of a subject. A common fault, to which he i 'ust 

 often plead guilty, is to use for the comparison data 

 over which the more experienced observer shakes his 

 head; they are too insecure to build extensively upon. 

 Yet even in this, theory may help observation by 

 showing the kind of data which it is especially 

 important to improve. 



I think that the more idle kinds of speculation will 

 hi avoided if the investigation is conducted from the 

 right point of view. When the properties of an ideal 

 model have been worked out by rigorous mathematics, 

 all the underlving assumptions being clearly under- 

 stood, then it becomes possible to say that such-and- 

 such properties and laws lead precisely to such-and- 

 such effects. If any other disregarded factors are 

 present, thev should now betray themselves when a 

 comparison is made with Nature. There is no need 

 for disappointment at the failure of the model to give 

 perfect agreement with observation ; it has served its 

 purpose, for it has distinguished what are the features 

 of the actual phenomena which require new conditions 

 for their explanation. A general preliminary agree- 

 ment with observation is necessary, otherwise the 

 model is hopeless ; not that it is necessarily wrong so 

 far as it goes, but it has evidently put the less essen- 



I tial properties foremost. We have been pulling at llie 

 I wrong end of the tangle, which has to be unravelled 

 I by a different approach. But after a general agree- 

 ' ment with observation is established, and the tangle 

 begins to loosen, we should always make ready lor 

 j the next knot. 1 suppose that the applied mathemati- 

 ! cian whose theory has just passed one still more 

 stringent lest by observation ought not to feel satis- 

 faction, but rather disappointment — " Foiled again ! 

 This time I had hoped to find a discordance which 

 would throw light on the points where my model culd 

 be improved." Perhaps that is a counsel of perfec- 

 ' tion ; I own that I have never felt very keenly a 

 j disappointment of this kind. 



Our model of Nature should not be like a building 

 ! • — a handsome structure for the populace to admire, 

 until in the course of time someone takes away a 

 corner-stone and the edifice comes toppling down. It 

 ; should be like an engine with movable parts. We 

 need not fi.x the position of any one lever ; that is to be 

 adjusted from time to time as the latest observations 

 indicate. The aim of the theorist is to know the train 

 of wheels which the lever sets in motion — that binding 

 of the parts which is the soul of the engine. 



In ancient days two aviators procured to themselves 



I wings. Daedalus flew safely through the middle air 



across the sea, and was duly honoured on his landing. 



Young Icarus soared upwards towards the sun until 



the wax which bound his wings melted, and his flight 



ended in fiasco. In weighing their achievements 



perhaps there is something to be said for Icarus. The 



classic authorities tell us that he was only " doing a 



stunt," but I prefer to think of him as the man who 



certainly brought to light a constructional defect in 



the flving-machines of his day. So, too, in science. 



Cautious Daedalus will apply his theories where he 



feels most confident they will safely go; but bv his 



excess of caution their hidden weaknesses cannot be 



brought to light. Icarus will strain his theories to the 



breaking-point until the weak joints gape. For a 



I spectacular stunt? Perhaps partly; he is often very 



\ human. But if he is not yet destined to reach the 



sun and solve for all time the riddle of its constitution, 



I vet he may hope to learn from his journev some hints 



I to build a better machine. 



Memorial Tributes to Sir Norman Lockyer. 



IN Sir Norman Lockyer the country loses one of 

 the most ardent supporters of science in his 

 time. As one who enjoyed his intimate friend- 

 ship for more than half a century, I would fain 

 add my personal contribution to the many ex- 

 pressions of regret and appreciation which the 

 loss is sure to call forth. 



There never was a man more thoroughly im- 

 bued than he with a sense of the importance of 

 the cultivation of science, not only for its own 

 sake, but also for the multitude of ways in which it 

 may be made to minister to the welfare of man- 

 kind. Though he had made choice of astronomy 

 as his own field of work, he was no mere special- 

 ist, but kept his sympathy in touch with the 

 progress of science as a whole, and worked, 

 harder than most of his contemporaries knew, to 

 further that progress. Sir Norman's younger 

 years as a clerk in the War Office, while affording 

 him an insight into the methods of a Government 

 Department, furnished also a training in business 



NO. 2653, VOL. 106] 



habits which served him in good stead through 

 later life. The secretaryship of the Duke of 

 Devonshire's Commission on scientific instruction, 

 to which as a young man he was appointed, un- 

 doubtedly gave the impetus that made him so 

 strenuous an advocate of a wider recognition of 

 the claims of science for a place in our educa- 

 tional and industrial organisation. This appoint- 

 ment, bv bringing him into personal acquaintance 

 with the leading men of science of the day, 

 strengthened and widened his sympathies. One 

 of the first results of the experience thus gained 

 was to convince him of the need for better teach- 

 ing of the rudiments of science in our schools. 

 He saw that one of the first requirements was 

 the production of simple elementary treatises on 

 the different departments of natural knowledge, 

 written not by mere book-makers, but by the best 

 living authorities on the several subjects. He 

 confided to me the scheme which he drew up, and 

 asked mo to co-operate with him. It so happened 



