February 22, 1906] 



NA TURE 



389 



lengths can be readily discovered ; these respond well to 

 the forces, and their tides must be the ruling semi- 

 diurnal tides of the oceans. The charts prove the existence 

 of large stationary oscillations. To doubt this fact would 

 be scarcely more reasonable than to doubt the existence of 

 the tide itself. The large ranges of tide imply critical 

 lengths, and critical lengths imply that the phase is con- 

 trolled by the resistance to the movement. 



In a second approximation it may be possible to take 

 into account the actual departures from critical lengths, to 

 make some numerical estimates of the resistance, and to 

 fix more accurately the modes of oscillation having regard 

 to the deflecting force of the earth's rotation. In my paper 

 ill.- latter effect has been considered only in reference to 

 arms or bodies of water tidally dependent upon larger 

 bodies. 



As soon as my critics develop their tidal theories 

 sufficiently far for making definite suggestions, I shall be 

 pleased and bound to give such developments careful con- 

 sideration. In the meantime, I believe that nothing is 

 gained by criticism which does not constantly revert to 

 such facts as have been brought out through observations 

 upon the tides. These constitute the final test of all 

 theories. R. A. Harris. 



Washington, D.C., January 26. 



It is Mr. Harris's theory with which we were, and 

 continue to be, at variance. We were unable to gather 

 the part played by this theory in the construction of his 

 series of cotidal charts, and hence our statement that this 

 construction was but "vaguely indicated"; but we are 

 glad to be assured that the theory has only been employed 

 in regions where observational data were entirely wanting, 

 and has not been allowed to vitiate, as we feared, results 

 obtained direct from observation. 



In reference to the phase theorem which we selected for 

 special comment, Mr. Harris now states that " the 

 large ranges of tide imply critical lengths, and critical 

 lengths imply that the phase is controlled by resistance." 

 The latter part of this theorem we are not prepared to 

 admit unless it be further contended that the critical con- 

 ditions implied are mathematically exact, especially in 

 consideration of the comparatively small frictional in- 

 fluences which can be brought to bear on the motions of 

 the sea. Any departure from the ideal critical state, and 

 we contend that such departures must inevitably occur in 

 a complex system like that of the ocean, will render the 

 determination of phase dependent on such departures as 

 well as on frictional influences, and we differ from Mr. 

 Harris in regarding the former rather than the latter as 

 the more powerful controlling influence in regard to phase. 

 Whence can the large resistances to motion, implied in 

 Mr. Harris's theory, arise? S. S. H. 



Atomic Disintegration. 



According to the investigations on radium, especially by 

 Prof. Rutherford, there can be no longer any doubt that 

 the formation of helium from radium is due to spontaneous 

 disintegration of the radium atom, and it is the same 

 with the other radio-active elements. Most competent 

 investigators have not hesitated to apply the same point 

 of view also to all the other elements. 



The enormous amount of energy set free in the form- 

 ation of helium — about io 9 great calories for a gram-atom 

 of helium — must render hopeless any attempts to reverse 

 this process. Considering the conformity of the other 

 gases of the helium type — neon, argon, krypton, and 

 xenon — it seems probable that they owe their existence to 

 a similar disintegration of atoms. It is not surprising, 

 therefore, that all attempts have failed to obtain a chemical 

 compound of those gases, and I do not think such attempts 

 likely to succeed in future. That, as yet, those gases, 

 excepting helium itself, have not been recognised as pro- 

 ducts of atomic disintegration may be due to their difficult 

 test. 



Now it seems to me there is nothing contrary to the 

 view that disintegration of atoms is an irreversible process, 

 strictly analogous to dissipation of heat. 



Considered in this way, there exists a parallelism not 

 only as regards the first law of' thermodynamics — conserv- 



NO. 1895, VOL. 73] 



ation of energy — with the principle of conservation of 

 matter, but also regarding the second law — dissipation of 

 energy, on the one hand, and atomic disintegration on the 

 other. And as it has been stated by Clausius that the 

 world's entropy tends towards a maximum, we may say 

 that likewise the quantity of free helium and the similar 

 " Edelgase " tends towards a maximum. 



This parallelism in material and energetical law appears 

 to me well worthy of notice. W. Meigen. 



Freiburg i/Br. 



Phosphorescence of Pyro-soda Developer. 



Some time ago (January, 1904) you were good enough 

 to publish a note on the " Phosphorescence of Photographic 

 Plates," and the following additional particulars of this 

 phenomenon may be of interest. The developer used is 

 the ordinary pyro-metol-soda solution. 



If a bromide plate is exposed in the camera, developed, 

 washed for a few moments only, and then placed in 

 aluminium sulphate solution in the dark, the picture be- 

 comes luminous and shows forth as a negative, the high 

 lights being dark, whilst the shadows are bright, the 

 darkest ones phosphorescing most strongly. If, however, 

 the plate (after having been exposed and developed) is 

 washed thoroughly for half an hour by means of a jet of 

 water under pressure, no phosphorescence is observed on 

 treating it with Al^SO,, solution, from which it appears 

 that a trace of the developing solution is necessary to cause 

 phosphorescence in the plate. 



If a few spots of unused developing solution are placed 

 in the bottom of a porcelain dish and A1,3S0 4 solution is 

 added (in the dark), the mixture will phosphoresce. But 

 if the developer has been used for developing exposed 

 plates, then its power of phosphorescence is weakened, and 

 if the same portion of solution is used repeatedly for 

 developing, and tested periodically for phosphorescence 

 between the developments, it will be found that its phos- 

 phorescing power is diminished after each development, and 

 that it finally vanishes altogether. This explains the pro- 

 duction of the phosphorescing negative. The most strongly 

 lighted part of the film is that which will destroy the 

 phosphorescing power of the developer it has absorbed, and 

 the unlighted portion or shadow is that in which the 

 absorbed developer will be least changed, and therefore 

 most strongly phosphorescent. 



The addition of various substances to the aluminium salt 

 modifies its phosphorescing power, and some prevent it 

 altogether, even when added in very small quantities. 

 Among those substances which strongly counteract the 

 phosphorescence may be mentioned the salts of thorium, 

 uranium, copper, lead, bismuth, iron, tin, cobalt, nickel, 

 chromium, zinc, cadmium, mercury, platinum, and silver 

 in the order named, while the salts of potassium, sodium, 

 ammonium, lithium, calcium, barium, strontium, mag- 

 nesium, and manganese seem to have little influence one 

 way or the other. 



The only substance found which has the effect of much 

 increasing the brilliancy of the phosphorescence is gold. A 

 solution of AuCl 3 alone, in fact, gives a more brilliant 

 phosphorescence than Al^SO.,. The gold is reduced to 

 the black metallic form, and while this reduction is pro- 

 ceeding light is emitted. Other reducing agents, however, 

 do not appear to emit any light during the process of re- 

 duction of AuCl 3 . The influence of the other metals on 

 the phosphorescing power of the gold solution seems to be 

 practically the same as for aluminium. 



Other aluminium salts, such as the nitrate, phosphate 

 (dissolved in HC1), chloride, &c, phosphoresce with pyro- 

 metol developer, but none so brilliantly as the sulphate. 



T. A. Yaughton. 



Ley Hill House, Sutton Coldfield, February 13. 



Emission of Light by Kanal-strahlen Normal to their 

 Direction. 

 In a former publication (Physik. Zeitschrijt, vi., 892, 

 1905) I have proved that the stream of positive ions which 

 form the Kanal-strahlen show the Doppler effect. In these 

 rays we have, therefore, a positive charge, and at the same 

 time velocity, and also, as a result of the vibrations of the 

 negative electrons, emission of light. Therefore it is 



