>7o 



NATURE 



\Fcb. 19, 1SS0 



myself the task to prove) there is not really more than one ex- 

 planation of the constitution of the ether in principle conceivable 

 [excluding, of course, the essentially endless vagaries about 

 "forces "J, then on this ground alone the hope may be enter- 

 tained by those who look to the existence of an explanation for 

 every physical fact, that difficulties that may naturally present 

 themselves at first will not prove insurmountable by a due amount 

 of thought and careful analysis. S. Tolyer Preston 



The Transverse Vibrations of Light 

 Few are probably likely to underrate the vast benefits which 

 have accrued to physical science since the time of Poisson, from 

 the application of mathematical analysis to physical problems ; 

 but it seems to me we are at present rather in danger of forgetting 

 that ;uch mathematical reasoning can only lead to useful results 

 when founded upon definite physical conceptions. It was upon 

 such a basis that the triumphs of Young, Fresnel, and Airy 

 were won ; and it is for want of such a basis that I fear we shall 

 get little aid from Mr. Tolver Preston's ingenious speculation. 

 Mr. Hicks has taken some exceptions to them, which seem sound 

 if he has correctly read the theory, though I am not quite sure 

 he has, or that I should go quite with him in regard to what Mr. 

 Preston may mean. But I wish to point out, with your permis- 

 sion, objections of a more simple and definite physical nature. 



The only transverse movements capable of being communicated 

 to an ether-molecule by transverse vibrations of matter, which do 

 not involve translation through a measurable though minute 

 distance in space, appear to be rotation on an axis, or (if we 

 conceive the molecule as an annuls) alternate contraction and 

 expansion — "vibration" Mr. Preston calls it— within its own 

 limits. In the case of a gaseous constitution, transverse transla- 

 tion in space with the assumed long free path, must continue, 

 and result in a free path different from the assumed direction of 

 the ray. The particles of sand employed to illustrate the 

 subject thus acquire a continuous transverse motion in passing 

 through the sieve, and do not "vibrate" or come back in an 

 orbit. Such true vibratory motion is the main characteristic of 

 solid bodies, and is the best known reason for conceiving the 

 ether as of a "solid" constitution. 



What I wish to point out is, that large classes of phenomena 

 appear to demand such actual transverse motion in orbits of the 

 entire ether particles, and cannot at present be explained without. 

 I confine myself to two of the simplest examples from polarisation. 

 It is well known that the production of complementary colours 

 from a plane polarised ray by a doubly-iefracting film and 

 analyser, may be simply represented to the eye and the mind by 

 the following diagram equation, which shows the resolution of 

 actual motions. 



Similarly, the two circularly-polarised rays in quart?, and their 

 conversion on emergence into a plane ray rotated on its axis by 

 the angular value of the difference in velocity, may be repre- 

 sented thus : — 



Here actual motions in the plane ab are resolved into two 

 opp isite circular motions represented by the doubly-barbed circle, 

 which meet on their emergence at the point R, to which their 



respective velocities from the common departure A have brought 

 them. There they are again resolved, the two tangential forces 

 T R destroying each other, and the two radial forces, R c, uniting 

 in the rotated plane wave, R p. Here again we have through- 

 out actual motions, through definite distances. And I am at a 

 loss to see how whole classes of phenomena of which these are 

 typical can be explained in any other way, or by any but a true 

 " vibration" bodily to and fro in space. If it be so, then it is 

 not enough for some vague physico-mathematical notion to satisfy 

 abstract mathematical conditions ; we must ask for the definite 

 physical conception which is to accou it for the physical pheno- 

 mena. Until we have this we have made no real advance in 

 comprehending the physics of the ether. 



At the same time I cordially agree with Mr. Treston in his 

 regret at the comparative distaste for the study of this subject ; 

 and I may, perhaps, add a suggestion on my own part, though 

 not leally new. To my own mind it seems as ea^y to conceive 

 of "matter" without gravity as with it, and of infinite elasticity 

 as of elasticity at all (which is not easy). In ponderable matter, 

 again, the most highly elastic solid bodies are as "solid" as the 

 least ; the greater mobility of their atoms by no means inter- 

 feres with that peculiarity of vibrating in orbils and preserving 

 a locus which distinguishes solids from fluids, and which so far 

 we have been obliged by the phenomena to attribute to the 

 ether also. Granted that to account for elasticity we have to 

 conceive atoms not in contact, and are confronted by the old 

 mystery of how they can act upon each other across a vacuum. 

 Still, does this confront us any more in the ether than in ponder- 

 able matter ; and, so far as they do go, are not our conceptions of 

 the one sufficient for and equally applicable to the other ? 



Lewis Wright 



Wellfield, Ashley Road, Crouch Hill, N. 



Diffusion of Copper in the Animal Kingdom 

 Je lis dans la Nature, vol. xxi. p. 305, un article intitule 

 " Diffusion of Copper in the Animal Kingdom," se termiuant par 

 ces mots: it is to be hoped that more extended observations will 

 inform us of the exact nature of the tble played by cupric com- 

 pounds in the animal economy. Je crois pouvoir satisfaire en 

 partie au moins a ce vceu. Dans plusieurs communications 

 inserees dans les publications des Academies des Sciences de 

 Paris et de Bruxelles (1878 et 1879), j'ai montre que chez certains 

 mollusques cephalopodes et gasteropodes et chez les crustaces 

 decapodes, le cuivre joue dans le sang le meme role physiologique 

 que le fer dans notre sang. 



Le sang veineux du poulpe (Octopus vulgaris), du homard 

 (l/omaru,), etc., contient une substance albuminoide incolore, 

 cuprifere, a laquelle j'ai donne le nom d'himocyan'ate, terme 

 rappelant sa parente avec l'hemoglobine. L' himocyanine forme 

 dans la branchie une combiuai-on peu stable avec l'oxygene ; cette 

 combinaison I'oxyhemocyanine est d'un beau bleu. Elle se deco- 

 lore en se dissociant sous l'influence du vide ou du contact avec 

 les tissus vivants. Aussi le sang arteriel du poulpe est d'un beau 

 bleu tant que l'animal respire une eau bien aeree. II suffit de 

 comprimer la branchie, de gener la respiration, pour voir le sang 

 arteriel se decolorer. 



L'hemocyanine parait avoir une constitution chimique analogue 

 a celle de l'hemoglobine. Comme cette derniere elle est suscep- 

 tible de se dedoubler en une substance albuminoide ne con tenant 

 pas de metal et en une substance cuprifere qui parait former des 

 sels crUtallisables analogues aux sels d'heinatine. 



Leon Fredericq 



Liege, le 1 1 fevrier, rue du pare, 25 



Lines of Force due to a Small Magnet 

 I HAVE been recommended by Sir William Thomson to send 



you the following construction for the lines of force due to a 



very small magnet. 

 The equation to the lines of force due to a very small magnet 



placed at the origin of co-ordinates and lying along the axis of 



x is — 



3/1 , = ' (I) 



(x-+y-)i C 

 By varying C we obtain a series of similar curves. 



Transforming to polar co-ordinates by puttiug x = r cos 9, 

 y = r sin 9, we get for the equation (1) 

 r = Csin c fl. 





