August ii, 192 i] 



NATURE 



/D 



getically the treatment can only be satisfactory 

 when their combined or reciprocal motion is 

 balanced about their common centre of gravity. 



Centres .of gravity, however, presumably dis- 

 appear from relativity ; and, what is more seri- 

 ous, so does the conservation of energy. For if 

 there is nothing absolute about speed there can 

 be nothing absolute about kinetic energy. The 

 relativity expression for kinetic energy contains 

 an arbitrary constant ; and whether energy is con- 

 served or not becomes a matter of convenience and 

 definition. The claim that relativity pressed to 

 extremes does away with all conservation, 

 as hitherto understood in physics, has been 

 seriously made by the eminent mathematician. 

 Prof. Hilbert, of Gottingen. On the other 

 hand, it might be replied, according to Sir 

 Joseph Larmor, that kinetic energy has 

 always been treated as relative to some 

 other body on which work might conceivablv be 

 done, and that the really invariant quantity is not 

 energy, but the integral of energy with time, 

 called " action " ; or as it may be regarded, per- 

 haps preferably for some purposes, i times angular 

 momentum. 2 For this appears to be independent 

 of frames of reference — which energy certainly 

 is not. 



Acceptance of the theory of relativity correlates 

 results, but does not explain them. The 



2 Which, by the way, is very suggestive of a constitutional gyrostatic 

 aether structure. 



theory does not even seek to explain or account 

 for phenomena : they just are so. It is not a 

 dynamical theory, it is a method of arriving at 

 results, like the second law of thermodynamics 

 and the conservation of energy. The full dyna- 

 mical explanation remains to be worked out, and 

 it may turn out to be on very much the old lines 

 along which we had previously regarded phvsical 

 phenomena. The true relation between aether and 

 matter, and how their interaction generates and 

 affects light, is an immense subject, not in the 

 least exhausted, and barely encroached upon, by 

 the perception that certain consequences inevi- 

 tably follow from an admission that the velocity of 

 light is a critical limiting velocity, which cannot 

 be exceeded, and which when compounded with 

 any other velocity retains its old value. 



\\^hether the properties of the aither can ever be 

 formulated in terms of the same sort of dvnamics 

 as we have found so fruitful and effective in deal- 

 ing with matter is at present an open question. 

 Quite possibly a different dynamics may be 

 needed, one perhaps of which we have as yet no 

 conception ; but let us not shut the door on dis- 

 covery, assume that nothing of the sort can ever 

 be arrived at, and think that pure mathematical 

 abstractions, glorified and complicated sufficiently, 

 can be an ultimate embodiment of physical laws 

 or can adequately express the facts of Nature. 



{J^o he continued.) 



The Conference of the International Union against Tuberculosis. 



THOSE who have followed the course of tuber- 

 culosis in this country have noted that 

 during the years of the war there was a sudden 

 interruption in the fall of the curves illus- 

 trating case-rate and death-rate from that 

 disease. Our work was. then in fields abroad. 

 Now, however, that we are getting back to 

 pre-war conditions, peoples and nations are 

 again joining forces in a new campaign against 

 tuberculosis in our civil populations, and at the 

 recent conference in London of the Inter- 

 national Union against Tuberculosis delegates 

 from forty nations, including China, Japan, 

 Persia, and Czecho-Slovakia, met to discuss the 

 great question of the cure and prevention of 

 tuberculosis. Science knows no national borders, 

 and it is obvious that the union is anxious to 

 work with men from all nations, and to this end 

 has drawn up a series of tentative regula- 

 tions in order that when German physicians 

 have composed the differences amongst themselves 

 arrangements may be made for their reception 

 into the councils of the union. The secretary of 

 the old International Association against Tuber- 

 culosis appears to have assumed that every- 

 thing would go on as before, and somewhat 

 injudiciously made an attempt to call the old 

 association together as a rival to the conference 

 of the union of Allies and neutrals held in Paris 

 last year. The wiser amongst his countrymen 

 • NO. 2702, VOL. 107] 



were against this, and at present the German 

 physicians are divided into two camps. For 

 the present the International Union is content 

 to make good its own footing, go its own 

 way, and lay down its own lines of operations, at 

 the same time leaving the regulations so elastic 

 that as asperities are smoothed down and diffi- 

 culties removed German workers may come in 

 and take their part in its great work ; and it is 

 hoped that steps towards this will have been taken 

 when the meeting is held in Brussels next vear, 

 or, at any rate, in \\'ashington two years later. 

 By that time the League of Nations may have 

 got under way, and the international character of 

 the union may have become complete. 



At the opening sitting of the London meeting 

 the Foreign Secretary, Lord Curzon, and the 

 Minister of Health, Sir .\lfred Mond, blessed in 

 no uncertain terms the ideals and work of the 

 union, and their presence no less than their works 

 may be accepted as of good omen that the Govern- 

 ment authorities will, in their anti-waste difficul- 

 ties, remember that a penny wise Health Ministry 

 may be pound foolish where the public health is 

 concerned, and that the same holds good as 

 regards the Board of Education. 



Prof. Calmette, in a most interesting opening 

 address characterised by all the clearness of vision 

 and beauty of expression for which this French 

 savant is noted, outlined a new hypothesis 



