Dec. 9, 1881.] 



KNOWLEDGE 



113 



John Milne, F.G.S. ' The glacial deposits of West Cumberland,' bv 

 J. D. Kendall, C.E., F.C.S." " 



It would be the ea-siest thing in the world to fill four or fire pages 

 ■weelcly with suih reports. Indeed, it is easier to use them than to 

 decline them ; but however excellent such things may bo in their 

 place, we must point out that they would not at all correspond with 

 the promises hcUl forth in our prospectus. When we increase our 

 space, it will be to find room for matter more likely to be widely 

 and generally interesting. Of course, the paper.^ read before our 

 learned societies are full of interest for experts in the respective 

 branches of science to which they belong ; and their subject matter 

 may be made veiy interesting by suitable treatment ; but their 

 mere names, or abstracts of their contents, could have no interest 

 for the great majority of our readers. Even our scientific readers 

 -would only be interested,- -each, perhaps, in one or two out of a 

 ■dozen Buch titles or abstracts. Riciiarh A. Proctor. 



TROFESSOR CLERK MAXWELL AND THE REVERSIBILITY 

 OF THE GRAMME MACHINE. 



[83] — Listening to Professor Sylvanus Thomjison's paper on 

 ■"Storage of Electricity," at the Society of Arts, last Wednesday, I 

 heard to my surprise the following story (as an introduction to his 

 subject) : — " Xot many months before he was seized with the 

 niortal illness which robbed us too soon of his rare and unique 

 ■genius. Professor Clerk Maxwell was asked by a distinguished living 

 man of science what was the greatest scientific discovery of the last 

 twenty-five years. His reply was, 'That the Gramme machine is 

 reversible. ' " 



Now I fully subscribe to Professor Thompson's statement about 

 the loss we have sustained by Professor Maxwell's death, of his rare 

 and unique genius ; but the latter part of the above citation I 

 listened to as to a story told of great men ; one of those stories 

 •which often have their origin in insignificant incidents or expres 

 eions, and are used for the purpo.se of raising the subject of which 

 the great man speaks in the estimation of the listeners, or are in- 

 tended to give a certain halo to his fame, and show his abstracted, 

 simple mind. A story of this latter category I heard told of Arago. 

 To enable a favourite cat to enter his study, he had a hole cut in his 

 door ; and when this cat had a kitten, he had a small hole cut at 

 the side of the big one, to give facility to the kitten also to enter. 

 We may look ujion such stories as the spice with which sometimes 

 scientific subjects are dished up ; and in that light I accepted the 

 «cc lunt of Professor Clerk Maxwell's opinion about the greatest 

 discovery within the last twenty-five years. 



But I was astonished to fiud this story printed in the paper as 

 rgiven in exten^o in the Society of Arts Journal, and hence offered to 

 the reader as an undeniable fact. 



Professor Thompson's paper itself contains the reason, why one 

 may doubt, that Professor Maxwell should have made such a reply 

 ■seriously ; and the reason is, that ever since Ritter built up his first 

 secondary pile, or Jacoby his first electro-magnetic engine, or 

 Oacinotti his electro-magnetic engine with the first ring armature — 

 nay, since Newton's law, as given by Professor Thompson himself in 

 his |>aper (" to every action there is an equal and contrary reaction "), 

 •was enunciated, there could be v_o doabt whatever that the Gramme 

 machine was reversible. But, principally, it follows directly out of 

 Lenz'a law of magneto-electric induction, published in 183'^, and 

 ■could have been foretold from all practical experience made with 

 the electro-magnetic jiower engine which was intended and expected, 

 some thirty to forty years ago, to supplant the steam-engine. 



We will set aside for a moment Newton's "immortal" law per se, 

 ■and its application to the secondary battery ; and take the phe- 

 nomena of the electro-magnetic motor, and of magneto-electric 

 induction alone, into consideration. 



Clerk Maxwell, in his " Electricity and Magnetism," 2nd edition, 

 section 530 (Vol. II., p. 167), gives the latter phenomenon in the 

 following wonls (under the heading Magneto-Electric Induction) : — 



'' in all cases the direction of the secondary current is such that 

 the mechanical action between the two conductors is opposite to the 

 fTirection of motion, being a repulsion When the wires are approach- 

 ing, and an attraction when thev are receding. This ven,^ important 

 fact was established by Leuz." '(Pogg. Ann XXI., 4S3.— 18;U.) 



Surely no great logical powers are required to interpret this law, 

 as, in fact, years ago it has been interpreted — viz., the same arrange- 

 ment of conductors and magnets which, by motion in relation to 

 each other will produce a cuiTcnt in the conductor, will produce 

 motion when from some electric source a current is sent through 

 the conductor. 



This "reaction" was applied in some of the earlier forms of 

 magneto-electric " induction machines," ^vhich were used for illus- 

 trating the aj>plication of electricity as a "moving power" ; and 

 P.icinotti, when describing his electric motor, in which the ring 



armature was for the first time applied (1860-6^1), stated already 

 that, when rotating the armature, his machine could be used as a 

 generator of electricity. 



Lastly, Jacobi showed nearly fifty years ago (about 1835 or 183G) 

 that the efficiency of electro-magnetic motors was seriously inter- 

 fered wiih by the electric cuiTents induced in the machine. Hence, 

 ever since the production of electric currents by means of magneto- 

 electric induction was underetood, and since the application of 

 electricity for the jiroduction of motion has been studied, there 

 could not have been any doubt about the reversibility of a magneto- 

 electric or dynamo-electric generator into an electro - magnetic 

 motor. And this story of ProfcsSor Clerk Maxwell declaring this 

 " discovery" as the greatest scientific discovery of the last twenty- 

 five years loses, to say the least of it, its point. 



Perhaps some of your readers can bring some further light to 

 bear upon this question, and witnesses will bo forthcoming to prove 

 either pro or con. 



I may incidentally remark here that Professor Thompson's paper 

 was the most complete account which it is possible to give of the 

 important question of the storage of electricity, as he has thoroughly 

 exhausted the subject in its scientific and practical bearing, for 

 which lie deserves the thanks of every electrician and engineer 

 interested in this latest phase of the development of the science of 

 elect ricitv. 



Xoi: 26, 1881. C. G. G. 



SUNDAY ART EXHIBITION. 



[84] — The exhibition of works executed by students of the City 

 School of Art, which was opened on two Sundays in December last, 

 having proved very interesting to a large number of people at the 

 East-end of London, we have great satisfaction in announcing that 

 arrangements have been made for again opening the exhibition on 

 Sundays. 



The Exhibition, which is the twenty-fifth Sunday Art Exhibition 

 opened under the auspices of the Sunday Society, will be held in 

 the Skinner-street Hall, Bishopsgate, and will be open from three 

 to six o'clock p.m. on Sundays, Dec. i and 11. Admission will be 

 free (without ticket), and we are pleased to be able to state that, in 

 addition to the work of the students, some valuable pictures from 

 the collection at South Kensington Museum will be exhibited. 



In order that the widest publicity may be secured for this effort 

 to provide innocent recreation on the leisure day of the week, we 

 ask you to insert this letter in j^our columns, seeing that the facili- 

 ties in London for visiting collections of art are far too limited, and 

 that the want of open museums and art galleries on Sundays is 

 especially felt by the inhabitants of crowded districts at this season 

 of the year, when our climate so often practically closes the parks 

 and gardens to them. — We are, 4c., 



William Rogers, M.A., Chairman. "( City School 

 R. H. Hadden, B.A., Hon. Sec. ) of Art. 



TH0M.4S Burt, M.P., President. \ Sunday 



Mark H. Judge, Hon. Sec. I Society. 



7, Conduit-street, W., Nov. 30, 1881. 



THE PYRAMID AND PARADOXERS. 



[85] — If I were called upon to classify paradoxers, according to 

 the good or evil effects they have had upon the community, I should 

 give the Pj-ramid craze a very honourable place, for it has served 

 to carrj- a knowledge of certain elementary facts connected with 

 astronomy and geometi-y into dark regions where attention to 

 such matters would probably never have been aroused by other 

 means. There are thousands, possibly I should be nearer the truth 

 if I said hundreds of thousands, who would never have known that 

 the pole of the earth's axis is moving amongst the stars if it had not 

 been for the Pyramid paradox, and the literature which has sprung 

 up around it. There seems to be something connected with such 

 speculations which has a fascination for a large class who would be 

 wearied by a more cautious search after truth. We have only to 

 notice how a statement, that three of the major planets will be in 

 perihelion next year, and, consequently, something e.'ctraordinar}' 

 may be expected to happen on the eartl(, goes the round of English 

 and Colonial papers, to see that such speculations are fitted to do a 

 sort of missionary work for science. 



I wish to enquire what attitude those who would like to see the 

 scientific spirit spread, shonlil take with regard to such speculations. 

 There are some who think that this tendency of human nature may 

 be utilised to obtain money for science; and they have not thought 

 it nnworthy of them, as seekers after truth, to pose before the 

 nninstmcted, as weather prophets or alchemists. Give us money to 

 study the sun, they say, and we will tell your fortune by snn-spots. 

 We will show that the elements are not elementary, and, perhaps. 



