December 29, 192 1] 



NATURE 



569 



I dissent completely, however, from his statements 

 that '* the criterion of this common-sense reality is 

 universality of experience," and that "the mongoose 

 was unreal because if the box were o{>ened nobody 

 would experience it." There is no such thing as a 

 universal experience, and nobody would experience the 

 mongoose, whether it was real or not. The only 

 things we experience are sensations and certain 

 processes^ such as judgments and emotions, which we 

 call mental. Each sensation or each judgment is 

 absolutely private to one individual. Other people's 

 sensations and judgments can be described to him, 

 but he can appreciate them only through other sensa- 

 tions of hearing and seeing, and these are just as 

 private as the first kind. Any satisfactory account of 

 scientific method must therefore rest at bottom on the 

 private sensation and the individual judgment. Other 

 people provide me with additional data, but I make 

 my decisions about them myself. 



The common-sense criterion of reality, I contend, 

 is that a large number of the sensations of the 

 observer can be described in terms of a small number 

 of assumed properties ot the object by means of 

 logically or mathematically simple laws. It is an 

 experimental fact that this is possible with respect to 

 many objects. In fact, the scientific notion of reality 

 is securelv based on experience, and cannot be altered 

 bv any argument or theory. Some realist philosophers 

 would probablv say that this criterion gives grounds 

 for believing that something is "real" in a different 

 sense from this ; but, like Dr. Campbell, I find myself 

 quite unable to understand what philosophers do mean 

 by "real." To me the above criterion is the defini- 

 tion of reality. The fly on this sheet of paper (at 

 the moment) is unreal because there are no sensations 

 that can be concisely described in terms of it. 



I question Mr. Hugh Elliot's assertion that 

 "materialism happens to be true." I do not deny it, 

 but I deny absolutely that Mr. Elliot knows it. Mental 

 operations may be a function of material ones, but to 

 find this out it would be necessary to show how all 

 mental phenomena can be inferred from physical and 

 chemical hypotheses, and this will never be known 

 until psychology is a complete science. Materialism 

 will be established, if at all, only at the very end of 

 science. At present it is pure metaphysics. 



Harold Jeffreys. 



St. John's College, Cambridge. 



Ix his article in Nature of October 20, p. 247, Prof. 

 Wildon Carr has maintained that the relativity theor\- 

 has made the reality of matter untenable. Later 

 writers have denied this. May I state the relation 

 of their views? 



Einstein refers the universe to a system of axes 

 fixed to an observer. The observer is a mind, and 

 hence Prof. Carr regards the material axes as also of 

 the nature of mind. The opponents of this view, 

 accepting the axes as material, regard mind as derived 

 from matter. The four axes of Einstein have no 

 physical counterpart in matter. But the relativists 

 have not envisaged any reality for the axes other than 

 a material reality. Therein, it seems to me, lies the 

 weakness of the relativist position. 



The four-dimensional universe of Einstein is a 

 hybrid made of mind (the observer) and matter (the 

 axes). The material axes are the measuring rods of 

 the observing mind. So long as we retain this hvbrid 

 character it is equally easy for opposing sides to claim 

 mind or matter as the fundamental reality. The meta- 

 physical definition of reality is that the ultimate is 

 the real — that is, that the entity from which all other 

 entities can be built up is the real. Science is not 

 only concerned with the real of common sense, as Dr. 

 NO. 2722, VOL. 10^ 



Norman Campbell seems to think, but is also concerned 

 with the real of metaphysics. The former may be 

 regarded as a horizontal section of reality and the 

 latter as a vertical section — the breadth and depth of 

 reality. 



What the relativists have to show to substantiate the 

 claim that mind is the ultimate reality is how to build 

 matter from mind. The axes of reference, and not 

 merely the origin, have to be of the mind-stufT. 

 Then the universe would be perceived as a universe of 

 mind-stuff. This is possible. A four-dimensional geo- 

 metry of a universe of mind-stuff has yielded me a 

 law of gravitation which is the analogue of Newton's 

 first law of motion and automatically solves the 

 problem of n bodies. The elaborate froth of the 

 Einsteinian tensor analysis for obtaining the law of 

 gravitation is due to the putting of the new wine of 

 mind into the old bottles of material axes. In the 

 four-dimensional universe of mind-stuff matter, space, 

 and time find their place as growths from mind. 



S. V. Ramamurty. 



Trinity College, Cambridge, December 9. 



Canon McClure's misconception is so fundamental 

 that I ask leave to correct it. If he had done me the 

 honour to read other of my writings, he would scarcely 

 have suspected me of a desire to banish imagination 

 from science. It is just because I maintain that the 

 imaginative element gives to science its highest value 

 that I think it important to distinguish carefully 

 between what is fact and what is imagination. I do 

 not "rule out, as scientifically invalid. Prof. Edding- 

 ton's being travelling with the velocity of light " ; but 

 I say that the perceptions of that being are not facts, 

 ascertainable by experiment ; and I protest against anv 

 exposition of relativity, or of any other scientific doc- 

 trine, which confuses laws, based mainlv on facts, 

 with theories, based mainly upon imagination. 



Norman R. Campbell. 



The Resonance Theory of Hearing. 



Is it possible for the ear to distinguish two notes of 

 the same pitch and of different quality sounding con- 

 currently ? 



Evidently it is possible. Of a number of examples 

 the following may be the simplest for experiment. 

 Hum any note with the teeth touching, but not 

 clenched. The performer may then hear the smooth 

 hummed note and at the same time another rough 

 note of the same pitch produced by the tapping of the 

 lower teeth against the upper teeth. (Stop the ears.) 

 Now imagine a tracing of the combined wave-form of 

 any two notes of the same frequencv to be submitted 

 to the Fourier analysis. The result of the analysis 

 must always be of the same nature ; there is no 

 alternative; "la solution est unique": — the complex 

 sound giving the periodic curve will be shown to be 

 made up of a series of pure tones of the harmonic 

 scale with frequencies », 2n, 3M, etc. If the ear acts 

 as a kind of "practical Fourier's theorem " it can per- 

 ceive only one fundamental tone. But we invariablv 

 judge of the pitch of a note by its fundamental tone. 

 If, then, we hear at the same time two notes of pitch 

 n, the ear must be able to perceive, also at the same 

 time, two fundamental tones of frequency n — that is 

 to say. it must be able to perform an analysis which 

 is not in accordance with Fourier's theorem. 



I mentioned this radical objection to the resonance 

 theory of hearing in iqi6 ("Questions of Phonetic 

 Theor}-, " p. 100), but nobody appears to have noticed 

 it. ^ W. Perrett. 



University College, Gower Street, W.C.i, 

 December 13. 



