December 2, 1922] 



NA TURE 



729 



of both commission and omission, due really to human 

 nature. It is well then that we should be provided 

 in this handy form with a clearly-written and common- 

 sense account of what scientific men mean by " science." 

 So much for the form . of the answer. As for its 

 content, Dr. Campbell will find one or other of his 

 statements disagreed with by each philosopher in turn. 

 But he refrains, wisely, from straying far along the 

 perilous paths of metaphysics, and, while expressing 

 his own opinion, admits frankly that there are others. 

 If the question is to be answered by way of definition, 

 Dr. Campbell's may be accepted as giving at any rate 

 one point of view : " Science is the study of those 

 judgments concerning which universal agreement can 

 be obtained." In rebutting the objection that there 

 cannot be universal agreement, Dr. Campbell selects 

 as the most perfect example the order in which events 

 occur. But have not some of the relativists suggested 

 that agreement on this may not necessarily be universal ? 

 Probably a definition is not the best way of answering 

 the question. Dr. Campbell's definition may be true, 

 but it does not cover the whole ground. It has one 

 advantage, in that it omits reference to " the external 

 world of nature," and that advantage is not merely 

 metaphysical but practical, since without further 

 discussion it permits one to include the study of the 

 human mind and its products. It has been the attempt 

 to define science by reference to its subject matter that 

 has led to much of the misunderstanding. Science is, 

 it seems to us, rather a way of looking at things or a 

 method of study, and if it excludes any subject it is 

 only because the method proves inapplicable. Un- 

 doubtedly a necessary condition is agreement upon 

 the judgments. Take literature for example. Purely 

 aesthetic criticism will never give that " Quod semper, 

 quod ubique, quod ab omnibus " which science demands; 

 and science therefore must decline to appraise the 

 poetic merits of " Lear," " Hamlet," and " Macbeth." 

 But the number of lines with weak endings in those 

 plays can be ascertained definitely, and can therefore 

 be subjected to scientific inquiry. 



How science works is the subject of three chapters, 

 which consider the nature, the discovery, and the 

 explanation of the laws of science. We used to be 

 taught that " a Natural Law is a regular sequence of 

 Cause and Effect." Dr. Campbell discards the causal 

 relation and .replaces it by " invariable association." 

 It is this invariability that lies at the base of the 

 definition of science recently given by the Master of 

 Balliol : " a body of generalisations from facts which 

 enables us to predict fresh facts." But further inquiry 

 shows that the associations, in their original sense, are 

 not invariable. Exceptions arise and have to be met 

 by new laws, either of the same kind or of a new type. 

 NO. 2770, VOL. I io] 



The discovery of a new type of law is the privilege of 

 genius. So far one may go with Dr. Campbell, but 

 when he implies that the genius imposes the law in 

 accordance with his " intellectual desires " and that 

 " the universe obeys the dictates of [his] mind," it is 

 not so easy to follow him. Does he mean that all our 

 systems are purely subjective ? To some extent the 

 answer to this question is given in the section headed 

 " Are theories real ? " The reality of a theory depends 

 on its power of predicting true laws, and thus it gains 

 universal acceptance. " A molecule is as real, and 

 real in the same way, as the gases the laws of which 

 it explains. It is an idea essential to the intelligibility 

 of the world not to one mind, but to all ; it is an idea 

 which nature as well as mankind accepts. That, I 

 maintain, is the test and the very meaning of reality." 

 The position is intelligible, but our difficulties recur 

 when we come to the interesting remarks on symbols 

 and the aesthetic sense of the mathematician — " one 

 more illustration of the power of pure thought, aiming 

 only at the satisfaction of intellectual desires, to control 

 the external world." Would it not be truer to say- 

 that the external world, by countless direct and indirect 

 means, acting since life began, has so influenced the 

 unconscious as well as the conscious perceptions of 

 man, that the mind necessarily regards as harmonious 

 those relations which conform to the seen or unseen 

 reality of the universe ? The scientific genius is he 

 who has a deeper intuition of that harmony than his 

 fellows, or, perhaps more accurately, he who can the 

 most easily raise to the plane of consciousness the 

 subconscious promptings of external nature. 



Aspects of Military Medicine. 



History of the Great War, based on Official Documents. 

 Medical Services: Diseases of the War. Vol. 1. 

 Edited by Major-General Sir W. G. MacPherson, 

 Major-General Sir W. P. Herringham, Col. T. R. 

 Elliott, and Lt.-Col. A. Balfour. Pp. viii + 550. 

 (London : H.M.S.O., 1922.) 215. net. 



UP to the beginning of the nineteenth century 

 the medical history of wars was very incom- 

 plete, and is to be found in memoirs or commentaries 

 written by individual military surgeons. To this 

 category belong the works of Percy, M'Grigor, and 

 particularly Barron Larrey, the great military surgeon 

 of the Napoleonic period. A great change, however, 

 took place with the publication by the Americans of 

 the splendid and exhaustive " Medical and Surgical 

 History of the War of Rebellion (1861-1865)," which 

 has remained a model for all later works on military 

 medicine. After the greatest of all wars it was to be 



Z I 



