August 26, 1920] 



NATURE 



801 



But not the less does he feel compelled to take 

 off his hat reverently before the shades of Gauss 

 and Riemann, and before those who have been 

 able to wield the mighty sword with which these 

 g-reat thinkers cut the knots that held physicists 

 back from the unrestricted calculus of to-day, 

 purified as it now is from the old assumptions. 



Now the importance of this thorough-going 

 application of the principle of the relativity of the 

 character of the point-event continuum to the 

 observer is obvious. It means relativity in signifi- 

 cance for intelligence. As Prof. Eddington has 

 recently remarked in a notable article in Mind, 

 the intervention of mind in the laws of Nature is 

 more far-reaching than is usually supposed by 

 physicists. He develops this conclusion in a 

 fashion which is impressive. Freundlich and Schick 

 in their recent books insist on the same thesis. 



But what does the word "mind" mean when 

 used thus? Not a substance in space-time, as 

 Prof. Alexander would have it. To start with, 

 such an assumption would involve either the rejec- 

 tion of the modern doctrine of relativity as the 

 school of Einstein has put it forward as dependent 

 on interpretation, or something tending towards 

 solipsism. Nor can mind mean substance in 

 another aspect, that in which Berkeley and the 

 Mentalists have sought to display it. Few com- 

 petent students of the history of thought look on 

 philosophy as shut up to such a view, the view 

 which New Realism seeks to bind into the "ego- 

 centric predicament." 



There is another interpretation of the meaning 

 of mind in which it signifies neither any of these 

 things nor yet an Absolute Mind apart from that 

 of man, but just our own experience interpreted 

 > being in every stage relative in its presentation, 

 and not so merely in the relation of measurement. 

 For Einstein's doctrine seems to be only a frag- 

 ment of a yet larger and even more striking view 

 of reality. Relativity is surely not to be confined 

 to judgments based on the co-ordinates we employ 

 in measurement. It may equally arise in other 

 instances from the uncritical applications of con- 

 ceptions concerned with quality as much as with 

 quantity. From such a point of view reality, 

 including human experience, is what it is only 

 because we are ever unconsciously, under the 

 influence of practical ends to be attained, limiting 

 our systems of reference, interpreted in even a 

 wider sense than that of Einstein. These may be 

 limiting ends imposed on us by the mere fact that 

 we are human beings with a particular position in 

 Nature. The relativity of knowledge will thus 

 assume the form of relativity of the real to 

 general points of view, and will result in a prin- 

 ( iple of degrees extending through all knowledge 

 NO. 26^2, VOL. 10^1 



and reality alike, which fall short of ideal comple- 

 tion. It is an old principle, as old as Greek 

 thought. If it is true, it solves many problems and 

 gets rid of the distinction between mental and 

 non-mental, between idealism and realism, be- 

 tween mind and its object. For it accepts the 

 "that," and confines the legitimate problem to 

 the "what." It also gets rid of the perplexing 

 idea of an Absolute Mind as something to be con- 

 ceived as apart from us while working in us. 



The idea and the method, recurring as they do 

 in ancient and modern philosophy, are worth 

 study by those who feel the stimulus of the new 

 atmosphere which Einstein has provided. They 

 may find a convenient analogue to the special 

 principle of relativity in Kant's "Critique of Pure 

 Reason," with its investigation of the general con- 

 ditions which are required in order to render any 

 individual experience possible. If they seek for an 

 analogue to Einstein's general principle, t!hey 

 may look either in the " Metaphysics " of Aristotle 

 or in the " Logic " of Hegel. The greatest thinkers 

 have presented resembling conclusions in varying 

 language. 



This path is one that is not easy to tread. It 

 is as hard to enter on as is that of the meta- 

 physician who has to try to understand the mean- 

 ing for philosophy of the absolute differential 

 equations which Einstein employs. Prof. 

 Alexander, however, knows the direction, if he 

 does not now look that way. And it may be that 

 the difficulties with which the new principle of 

 general physical relativity seems to threaten New 

 Realism, with its non-mental and static reality, 

 may lead him, with his openness of mind, 

 to consider once again whether he should not 

 wend his steps afresh towards the wicket-gate 

 for a further pilgrimage. But whatever the direc- 

 tion in which he is looking, his new book is full 

 of stimulating material, even as it stands. 



Haldane. 



Principles and Practice of Surveying. 

 Surveying. By W. Norman Thomas. Pp. 

 viii -1-536. (With Answers.) (London: 



Edward Arnold, 1920.) Price 315. 6d. net. 



ALL British surveyors will give the heartiest 

 welcome to this excellent book. We have 

 become accustomed to American and German 

 survey literature, and have relied too much upon 

 it. The author has gone far to relieve us of this 

 necessity. He succeeds admirably in emphasising 

 the importance of a due appreciation of the errors 

 involved, and his mathematical investigations and 

 notes on the accuracy of each method are clear 

 and convincing. 



