3Q^: 



NATURE 



[May..5,..i92i 



that for practfc^l, /.utUitajrian purposes co-ordinated 

 study of the tidal phenomena at coastal observatories 

 would be of greater value. The official predictions, 

 based on extended local observations, attain such a 

 remarkable degree of accuracy that the error is, in 

 what we may term by courtesy normal weather, 

 negligible. The trouble is that it is the unexpected, 

 in the form of wind and barometrical change at 

 critical times, that happens, and we have no formulae 

 at hand with which to apply corrections to predictions. 



The question is : If, by study and observation, it 

 should prove possible to discover such formulae, could 

 we communicate the results to those concerned on 

 incoming ships and in harbour in time to be of ser- 

 vice? So far as the effect of barometer gradients 

 is concerned the answer will probably be " Yes, with 

 wireless telegraphy at our command." But the wind 

 factor is a different matter, its influence being depen- 

 dent upon the change in direction and velocity relative 

 to the time of high water within the area of influence. 



While barometric pressure will be effective to the 

 same extent at any point of the water surface of the 

 globe, I think it may safely be asserted that the 

 influence of the wind on the primary ocean tides will 

 be negligible as compared with its effect on coastal 

 tides, enormously as they are increased by comparison, 

 and converted into currents by land resistance and by 

 the opposing head of outflowing rivers, often en- 

 hanced by rainfall — another factor to be considered. 



The lack of encouragement of scientific investiga- 

 tion in this particular department of science is most 

 striking. A. C. Tennant. 



I AM indebted to the Editor for permission to* com- 

 ment on Mr. Tennant's letter. It does not call into 

 question any of the statements of my article, for I 

 did not deny the great importance at the present 

 time of a study of the iidal phenomena at cAastal 

 observatories. As a matter of fact, practica,ny all 

 the resources of this institute are at present devoted 

 to this kind of study. 



As regards the prediction of coastal tides, I may say, 

 by way of example, that for Liverpool the dis- 

 crepancies between observation and official prediction 

 of high water possess an oscillation which reaches a 

 foot in range. The prediction-error of any high water 

 differs, as a rule, much more from that of the next 

 high water than it does from that of the next but 

 one. Further, when the complete tide is predicted 

 from the results of all the analyses that have been 

 made, there is a discrepancy with observation which 

 possesses semi-diurnal and quarter-diurnal oscillations 

 often exceeding a foot in range. The periodicitv of 

 these discrepancies indicates an astronomical origin, 

 but as they are of a very complicated nature and are 

 superposed on the irregular weather-effects, it is often 

 impossible at present to say exactly how much of any 

 discrepancy is due to departure from " normal 

 weather." Herein lies one of the difficulties of study- 

 ing the weather-effects. J. Proudman. 

 «. Tidal Institute, Liverpool. 



The Physical Continuity of "Space." 



The turn which the letter of Dr. Jeffreys (Nature, 

 April 28) has given to the "'space' or 'aether'?" 

 controversy may easily obscure the real point at issue. 

 The clear import of my letters of April 7 and 21, and, 

 I think also, of Prof. Eddington's forceful apprecia- 

 tion of the questions involved (April 14), is that the 

 physical universe — at bottom a universe of energy — 

 must in some form or other be cc«itinuoiisly extensive, 



NO. 2688, VOL. 1072 



and cannpt be discrete. The metaphysical necessity is 

 that something physical must constitute interstellar 

 "space." The contention is not primarily one ot 

 defending the electro-magnetic aether, or any other 

 specific aether, but of providing for extension through- 

 out the universe. If those who doubt or deny the 

 existence of a connecting medium in any sense hitherto 

 understood, can show that light, electricity, gravita- 

 tion, or any other manifestation of energy themselves 

 constitute the regions of interstellar, or interplanetary,, 

 "space " in such a way that extension is always pre- 

 served, then I, for one, am perfectly satisfied. But let 

 them not be responsible for language, or omissions of 

 language, that inevitably lead to the implication of 

 "emptiness" in a universe of transferable energy. 

 It is when the outstanding question of paramount 

 interest from the points of view of both physics and 

 metaphysics, namely, " Of what does interstellar 

 'space' consist?" is ignored that the situation 

 becomes intolerable. 



Dr. Jeffreys will agree that if relativity has indi- 

 cated anything clearly it is that no rigid line of 

 demarcation can be drawn between the provinces of 

 physics and metaphysics. As Prof. Eddington indicated 

 very clearly in his letter of April 14, in the last resort 

 we are driven back on a theory of extension ; and it is 

 surely incumbent upon those who say that the 

 mechanics of the universe can be explained without a 

 physical aether to show how the conception of "empty 

 space " as an entity in Nature, which not only 

 amounts to a contradiction in terms, but is also 

 entirely discountenanced by the theory of relativity 

 itself, can be avoided. 



It should be observed that I assume the ultimate 

 entity in the universe to be energy — that physical 

 power which, in effecting changes on a background 

 of extension, introduces the idea of motion, and hence 

 of velocity and time. And since inertia is now known 

 to be a property of energy, the ground is actually 

 prepared for those who shout "Away with the aether ! " 

 to save an awkward situation by representing the 

 whole of this universe of energy in a theory of exten- 

 sion. L. C. \V. Bonacina. 



May 1. 



Logs and Antilogs. 



On p. 7 of Nature of March 3 a recommendation 

 is mentioned that when taking out the number corre- 

 s[x>nding to a logarithm a table of antilogs should 

 be used. Assuming the usual seven-figure work, the 

 opposite course should be followed, because the com- 

 puter can then write down five figures at once and 

 add the remaining two by means of the difference 

 table ; no addition or crossing out is required. Thus 

 for the logarithm 0-1234567 the log table gives 

 1-3287 for 1234269, and 298 in the 327 difference table 

 gives 91, so we write 1328791. Vice versa, having 

 1-328791, what is the logarithm? The anti-table gives 

 12345 ^t once, whilst the difference 20 gives 67, so 

 that we write 1234567. No figure requires alteration 

 and the work is done with a minimum of mental strain. 



As one who does a great deal of computation, let 

 me state that my order of preference for usual work is 

 Cotsworth's multiplication table (which is better than 

 Crelle's), then the Triumphator or Brunsviga cal- 

 culating machine, then Shortrede's table, which in 

 one volume gives both logs and antilogs ; but special 

 tables can also be usefully employed. Thus Bottomley 

 for all four-figure work is still the best ; for multiplying 

 two figures by four, Peters 's table; and for two figures 

 by three, Zimmermann's. 



