394 



NATURE 



[May 26, 192 1 



factory results may be obtained by means of a sound- 

 ing wire attached to a heavy block of concrete or box 

 of stones (see Science, vol. xlii., 1904, p. 704), 



Those members of the new Challenger expedition 

 whom fortune may choose to be responsible for the 

 tidal observations have it in their hands to make all 

 tidal workers using their data everlastingly grateful. 

 This gratitude they may secure by insisting that the 

 tidal observations should be made in Greenwich mean 

 civil time, reckoning the hours from o to 23. Apart 

 from the many advantages for purposes of computation 

 resulting from such procedure and the ease with which 

 time comparisons of the tide at different places may 

 be made, there is one outstanding advantage — it will 

 remove all uncertainty as to the kind of time used. 

 Many otherwise excellent tidal observations are of 

 little use because there is no certainty as to the kind 

 of time employed, whether mean local civil, mean 

 local astronomical, local apparent or standard time 

 for some unknown meridian. The use of Greenwich 

 mean civil time should prove further desirable in view 

 of the change to this kind of time soon to be made in 

 the Nautical Almanac published by the British Ad- 

 miralty. H. A. Marmer. 



U.S. Coast and Geodetic Survey, Washing- 

 ton, D.C., April 15. 



The Physical Status of " Space." 



To answer all Mr. Bonacina's points (Nature, 

 May 5, p. 300) is not possible in a single letter. I 

 agree with him that no rigid boundary can be drawn 

 between the provinces of the older physics and meta- 

 physics. Concepts are freely introduced into both 

 which are not known to experience, and are never 

 used either in describing past experience or in 

 inferring future experience. Some hypotheses are 

 necessary in any science, but hypotheses that are 

 never used are neither necessary nor useful. The 

 elastic solid aether forms an excellent example of 

 these. It is assumed that electric and magnetic 

 forces satisfy certain differential equations, and this 

 is the only assumption required for the theory of the 

 propagation of electromagnetic waves. The aether 

 theory, however, introduces the additional hypothesis 

 that one of these forces is a displacement in an elastic 

 solid the properties of which differ from those of any 

 ordinary solid. This assumption is never used, has 

 no basis in experience, and cannot be tested experi- 

 mentally. Accordingly I say it should not be made, 

 for the introduction of additional hypotheses decreases 

 the probabilitv of the theory. The other assumption, 

 which is valuable and leads to much new know- 

 ledge, makes no mention of an aether. It appears to 

 be the case that all so-called explanations of physical 

 laws by means of the aether are really based on some 

 mathematical assumption that makes no reference to 

 an aether at all. 



I cannot see Mr. Bonacina's difficulty about 

 "empty space." I have advanced no theory involving 

 any such entity, and think that space is as useless a 

 concept in physics as aether. To construct a space 

 with suitable properties may be an aim of physics, 

 but it is certainlv not the starting point. The exist- 

 ence of entities incapable of being objects of experi- 

 ence_ is a thornv problem even to metaphysicians, and 

 I think that physicists would do well to postpone its 

 consideration so far as possible until they have some 

 idea of the basis in their knowledge of the proposi- 

 tions to which they attach high probabilities. 



Dr. Camobell's point CMay 5, p. 301") is dealt with 

 in the article (Nature, February 17) of which I was 

 part author. Geometry is not the measurement of 

 NO. 2691, VOL. 107] 



the earth, and never was ; it was pointed out in the 

 article that that excellent idea in nomenclature was 

 never carried out. Euclid's geometry was, from the 

 nature of its constructions and postulates, quite in- 

 applicable to earth measurement. If anyone doubts 

 this, let him consider the definitions and axioms as 

 they stand and see how many of them are verifiable 

 in. even a few cases on a scale such as occurs in 

 surveying. Further, Euclid's treatment assumes 

 that the postulates are true in all cases. To 

 suggest that this can be known by experiment is 

 ridiculous. It is at best an inference to which a high 

 probability can be attached. I know of nobody but 

 Einstein and his followers who has used the word 

 "geometry" in any other than the mathematical 

 sense. The measurement of the earth is always 

 known as "geodesy," and has been for more than a 

 century; and measurement in general is "mensura- 

 tion," the most important and least discussed of all 

 sciences. Constancy in terminology requires that 

 these meanings should be retained. Dr. Campbell 

 would scarcely claim that measurement in general 

 should be called " geometry " in his sense. 



Harold Jeffreys. 



The Reparation Act and Scientific Research. 



Prof. Gardiner (Nature, May 19, p. 359) is one 

 of many British men of science who are helping to 

 pay the German war indemnity. One does not obtain 

 goods from Germany unless one is compelled ; it is 

 difficult to see how standard German books and new 

 publications can be procured from home industries, and 

 they are necessary to research. In other cases the goods 

 might be expected to be made by British firms. For 

 many months I have been trying to obtain Wollaston 

 wire of a certain diameter from a well-known British 

 firm. ,At first I was informed that it could not pos- 

 sibly be made. I had bought it before in Germany, 

 so they tried to make it. Several samples were un- 

 satisfactory, and finally I was told that the British 

 firm did not wish to make any further attempts. I 

 then ordered some of the German wire, which I was 

 required to pay for in advance, for the reason stated 

 bv Prof. Gardiner*. This was reasonable, as the price 

 charged by the German firm, plus indemnity which I 

 pay, is less than I have been paying for unsatisfac- 

 tory wire in England. The wire was on the way for 

 several weeks. Meanwhile work was delayed. The 

 Customs officials know nothing of the reduction of 

 the tax from 100 per cent, to 26 per cent., announced 

 bv Mr. Chamberlain. Another order for new books, 

 given in February, was dispatched from Bonn on 

 March 4, and arrived in London on April 12 and 

 April 16. Notice from the Customs was received a 

 month later. After two days spent at the Customs 

 filling up forms, and five letters requesting delivery, 

 I still await the latter. 



The condition of the British man of science who 

 elects to do research will soon become impossible. 

 Perhaps that is really the idea behind all this. The 

 extension of the "key industry" idea will finish us 

 altogether. " J. R. Partington. 



East London College, University of London, 

 Mav 20. 



The Resonance Theory of Hearing. 



I SHOULD like, in the first place, to take this oppor- 

 tunity of thanking Dr. Perrett for his reply in Nature 

 of May 5 (p. 301), but I feel difficulty in accepting the 

 explanation he there advances on the displacement 

 hypothesis, because it does not seem to me to fit in 



