Jan. 29, 1880] 



NA TURE 



H5 



I have not thought it expedient to delay the publication of the 

 letter on the chance that something bearing on the subject might 

 be found among Maxwell's papers. 

 (Copy.) 



Cavendish Laboratory, 



Cambridge, 



19th March, 1S79 

 Sif, 



I have received with much pleasure the table; of the satellites 

 of Jupiter which you have been so kind as to send me, and I am 

 encouraged by your interest in the Jovial system to ask you if 

 you have made any special study of the apparent retardation of 

 the eclipses as affected by the geocentric position of Jupiter. 



I am told that observations of this kind have been somewhat 

 put out of fashion by other methods of determining quantities 

 related to the velocity of light, but they afford the only method, 

 so far as I know, of getting any estimate of the direction and 

 magnitude of the velocity of the sun with respect to the lumini- 

 ferous medium. Even if we were sure of the theory of aberra- 

 tion, we can only get differences of position of stars, and in the 

 terrestrial methods of determining the velocity of light, the light 

 comes back along the same path again, so that the velocity of 

 the earth with respect to the ether would alter the time of the 

 double passage by a quantity depending on the square of the 

 ratio of the earth's velocity to that of light, and this is quite too 

 small to be observed. 



But if J E is the distance of Jupiter from the earth, and / the 

 geocentric longitude, and if /' is the longitude and A the latitude 

 of the direction in which the sun is moving through ether with 

 velocity v, and if V is the velocity of light and I the time of 

 transit from J to !•", 



J E = [V - v cos A cos (/-/')] /. 

 By a comparison of the values of t when Jupiter is in different 

 signs of the zodiac, it would be possible to determine I' and v 

 cos A. 



I do not see how to determine A, unless we had a planet with 

 an orbit very much inclined to the ecliptic It may be noticed 

 that whereas the determination of V, the velocity of light, by 

 this method depends on the differences of ] E, that is, on the 

 diameter of the earth's orbit, the determination of v cos A 

 depends on J E itself, a much larger quantity. 



But no method can be made available without good tables of 

 the motion of the satellites, and as I am not an astronomer, I 

 do not know whether, in comparing the observations with the 

 tables of Damoiseau, any attempt has been made to consider the 

 term in v cos A. 



I have, therefore, taken the liberty of writing to you, as the 

 matter is beyond the reach of any one who has not made a 

 special study of the satellite-. 



In the article E [ether] in the ninth edition of the " Encyclo- 

 paedia Britannica," I have collected all the facts I know about 

 the relative motion of the ether and the bodies which move in 

 it, and have shown that nothing can be inferred about this 

 relative motion from any phenomena hitherto observed, except 

 the eclipses, Ace, of the satellites of a planet, the more distant 

 the better. 



If you know of any work done in this direction, either by 

 yourself or others, I should esteem it a favour to be told of it. 

 Believe me, 



Yours faithfully, 

 (Signed) J. Clerk Maxwell 



D. P. Todd, Esq. 



' Linnean Society, January 15. — Prof. Allman, president, in 

 the chair. — Mr. A. J. Hewett exhibited and made remarks on a 

 common web on community of cocoons, and of the moths (genus 

 Anaphe?) escaped therefrom, said to have been got at Old 

 Calabar. — Mr. Baker brought under notice a monstrous form of 

 Thistle ( Carduus crispus) obtained by the Rev. J. A. Preston 

 in Wiltshire. In this specimen the capitula were abnormally 

 numerous, and aggregated in secondary heads as in Echinops. — 

 A Moa's tibia aud tarsus (Dinornis maximtu) dug up four feet 

 from the surface at Omaru, N.Z., were shown on behalf of Mr. 

 Jas. Forsyth. — A paper was read on the birds and mammals 

 introduced into New Zealand, by Mr. H. M. Brewer. The 

 author refers to Ur. Buller's Avifauna of New Zealand as not 

 written too soon, for the rapid disappearance of many highly 

 interesting forms is to be deplored. Finches and other small 

 birds introduced arc preyed on by the New Zealand Owl, 

 bnt nevertheless quite a long list of British songsters, game 

 birds, and others have been successfully established. Pheasants 



in some districts abound; and it is observed that when the tremor 

 of an earthquake occurs the cock pheasants set up a continuous 

 crow, either of defiance or fear (?). Partridges thrive best on 

 the south island. Red deer are now seen in herds on the hills 

 near Nelson. Hares have increased too rapidly, and the female 

 in New Zealand has become more prolific, giving birth to six or 

 seven young at a time. Kangaroos and various other mammals 

 have likew is? been imported, but unfortunately facts mentioned 

 point out that the acclimatisation of some of them is not alto- 

 gether an unmitigated blessing to the farmer colonist. — Then 

 followed a memoir by Mr. J. G. Baker "Synopsis of the Aloineie 

 and Yuccoideie." To these two tribes belong all the shrubby 

 arborescer.t tribes of the capsular Liliacea;. Aloes belong en- 

 tirely to the Old World ; out of a total of 200 species 170 being 

 concentrated at the Cape of Good Hope, the remainder in the 

 highlands of Tropical Africa. Of the Yuccoidea: there are about 

 fifty species altogether, and nearly all are natives of Mexico and 

 the Southern United States. The yuccas fruit rarely under cul- 

 tivation, the large white pendulous flowers being in the wild 

 plant fertilised by a moth of the genus Prcnuba. Ilcrreria, 

 belonging to temperate South America, is a shrubby climber 

 with the habit of Smilax and Diosrorea. — Messrs. J, Poland, J. 

 Darell Stephen-, and Prof. Allen Thomson were elected Fellows, 

 and T. Jefiery Parker, an Asociate of the Society. 



Zoological Society, January 6. — Prof. Flower, F.R.S., 

 president, in the chair. — Prof. Newton, F.R.S., V.P., exhibited, 

 on behalf of Mr. G. B. Corbin, a specimen of Acanihyllis she 

 Chtctura caudacu/a — the Needle-tailed Swift — shot near Ring- 

 wood, in Hampshire, in July, 1879, remarking that it was the 

 second example of this Siberian species which had been obtained 

 in England. — Mr. John Henry Steel, F.Z.S., read a series of 

 preliminary notes on the individual variations observed in the 

 osteological and myological structure of the Domestic Ass 

 (Eqitus ashms). — A communication was read from Mr. E. W. 

 White, C.M.Z.S., containing notes on the distribution and 

 habits of Cltlamyphorus tritncatus, from observations made by 

 the author during a recent excursion into the western provinces 

 of the Argentine Republic, undertaken for the purpose of ob- 

 taining a better knowledge of this animal. — Dr. John Mulvany, 

 R.N., read a paper on a case which seemed to him to indicate 

 the moulting of the horny beak in a Penguin of the genus 

 Eudyptes. — Mr. O. Thomas, F.Z.S., read the description of a 

 new species of Alus, obtained from the Island of Ovalau, Fiji, 

 by Baron A. von Hiigel, and proposed to be called Afus huegtli, 

 after its discoverer. — A communication was read from Mr. R. 

 G. Wardlaw Kamsay, F. Z.S., containing a report on a collec- 

 tion of buds made by Mr. Bock, a naturalist employed by the 

 late Lord Tiveeddale, in the neighbourhood of Padang. Three 

 species were described as new, and proposed to be called 

 Dicntrus sumatianus, Turdinus marmoratus, and Myiophoneus 

 castaneus.— Dr. Gunther, F.R.S., read a description of two 

 new species of Antelopes, of the genus Neotragus, N. lirki, 

 from Eastern Africa, and A r . mclaris, from Damara-land. 



Geneva ; 



Society of Physics and Natural History, May 1, 1S79. 



M. Charles Soret details his experiments for investigating the 



mode of distribution of salts in solutions, the constituents of 

 which are subjected to different temperatures. The attempts 

 made upon azotate of potash and chloride of sodium led him to 

 the discovery that there is a greater concentration in the cold 

 part than in the warm. 



June 5. — Prof. Schiff discusses the comparative properties of 

 the nerves of sense and those of motion. He demonstrates on 

 a curarised frog, the persistence of sensibility after the animal 

 has lost all capacity for movement under the action of the poison. 

 He observes, at the same time, that the persistence is only 

 relative, and that the sensibility presently disappears, after an 

 interval varying in duration according to the temperature. If 

 that temperature is low (3° or 4 C, for example) the frog may 

 live for eighteen days. — MM. L. Soret and E. Sarasin have 

 determined the principal elements of the magnesium spectrum, 

 by measuring the refraction indices of quartz for its principal 

 lines, and by the existence of numerous photographs. — M. G. 

 Lunel describes a new species of Trygonide belonging to the 

 genus Pteroplatea, brought from Rio Janeiro. — M. R. Pictet 

 reports his investigations to solve the problem — What form must 

 be given to a definite surface that it may maintain its equilibrium 

 in the air with the minimum of mechanical work ? His experi- 

 ments were made with kites having a dynamometer of great 



