>//. 4. 1872J 



NATURE 



181 



plucked a mussel from the rock knows better in this 

 respect- thm Dr. Brehm ; and when the latter tells us, 

 a propos of the songs of birds (p. 37), that the " voice is 

 still motion." and wu connect the statement with a pre- 

 vious assertion (p. 19), that "worlds roll on through 

 boundless space — and live," we feel certain that we ought 

 to hear the music of the spheres, or some other mystical 

 sweet sounds, if we could only elevate ourselves to his 

 exalted ecstasy. 



But we think we need not trespass further on the time 

 of our readers. We will conclude by e.xpressing the 

 hope that when Mr. Jesse and Mr. Labouchere next set 

 about translating a German author they will have better 

 luck in pitching upon a subject — and they will easily find 

 one — for their labours than the rhapsodies of Dr. Alfred 

 Kdmund Brehm. 



OUR BOOK SHELF 



Proceeiiings of the London Mathcmatual Soiietv. \'ol. 



iii., Nos. 21 — 40. 

 The papers read before this .Society still preserve the high 

 character attributed to them in the notice of vol. ii., which 

 appeared in this journal. That such should be the case is 

 not matter for surprise, when we run our eyes over the list 

 of contributors. The principal authors are Prof. Cayley 

 and Mr. Samuel Roberts. The former furnishes three 

 memoirs on cjuartic surfaces (pp. 59 — 69 ; 19S — 202 ; 234 — 

 266) ; sketch of recent researches upon quartic andquintic 

 surfaces ; rational transformation between two spaces 

 (pp. 127 — 180) ; on Plucker's models of certain quartic sur- 

 faces. The latter communicates papers on the order of 

 the discriminants of a ternary form ; pedals of conic s.ec- 

 tions (pp. 88— 98) ; on the ovals of Des Cartes (pp. 106 — 

 126) ; on the order and singularities of the parallel of an 

 algebraical curve (pp. 209 — 259) ; on the motion of a plane 

 undercertain conditions. Prof. Clerk Maxwell contributes 

 a paper on the mathematical classification of physical 

 quantities. Besides the forej;oing communications, the 

 above-named gentlemen have laid other papers before the 

 Society. Memoirs have also been presented by Mr. J. 

 Griffiths, Mr. J. J. Walker, Prof Clifford, Hon. J. W. 

 Strutt, and other members. Some other highly valuable 

 communications, we learn from the " Proceedings," were 

 made to the Society, but no record has as yet been nude 

 of them, their authors not having yet sent their completed 

 papers for publication. The Society, from the number 

 and high character of its memoirs, seems to have met a 

 want, and is, perhaps, the only Society before which many 

 of the communications could have been brought. As 

 generally the papers are worked out in some detail at the 

 meetings, members have an interesting opportunity of 

 seeing how some of our foremost mathematicians employ 

 their divers instruments. The Society has lost by death 

 during the past session, its first president, and one of its 

 earliest warm supporters. A slight sketch of Prof. De 

 Morgan and his works appeared in N..\ 1 URE close upon 

 his death in March last. The eighth session of the 

 Society's existence has just commenced, and we trust its 

 future work may be as good as that it has already 

 achieved, Floreat. 

 Treatise on Terrestrial Magnetisvi. (Blackwood and 



Sons.) 

 The first half of this book contains a good deal of in- 

 formation, and some inquiriesconnected with the question 

 of the secular variations in the magnetic elements. The 

 author, on the supposition that the secular changes in the 

 declination are caused by the action of a single, slowly 

 rotating pole on a needle which at each place is locally 

 influenced in a definite and determinable mani.er, com- 



putes the declination at several places, and shows that it 

 agrees tolerably well with actual observation. The ro- 

 tating pole he places at a constant distance of 23^ 30' from 

 the pole of the earth's axis, and gives to its rotation a 

 period of (140 years. The latter part of the book, how- 

 ever, is taken up with "an hypothesis." The writer of 

 this book, and many other such writers, would do well 

 to remember the words of Newton, '^Hypotheses noii 

 Jingo." The hypothesis referred to is simply this :• — that 

 the sun attracts the electric matter in the earth and carries 

 it round in a sort of tidal wave, this causes an electric 

 current from east to west, which causes the magnet to 

 point to the north, and from which the writer also attempts 

 to deduce some of the other phenomena of magnetism. 

 There seems to us to be some ambiguity in the writers 

 method of expression, so that we do not clearly gather 

 whether he intends this current to account for the whole 

 magnetic action of the world, or only for the variations of 

 it. A consideration of the character of the variations 

 of the needle is sufficient to overthrow the hypo- 

 thesis announced by our author. The solar diurnal 

 variation is thus explained by him : — The pole of the 

 ecliptic revolves once a day round the pole of the earth's 

 axis, the needle tends to follow this, and hence the solar 

 diurnal variation. Now, we may point out a circumstance 

 which, apparently, entirely overthrows, not only this 

 hypothesis, but any which attempts to account for that 

 variation by anything of the nature of the movement of 

 a magnetic pole. At Point Barrow the needle points N.E., 

 at Port Kennedy it points .S.W., yet at each place the 

 solar diurnal variation follows local time and exhibits pre- 

 cisely the same features. .Standing, then, at the centre of 

 the needle, and looking towards its marked end, that end 

 would at both places be observed to be moving towards 

 the left hand of the observer between the hours of 8 A M. 

 and I P.M. But since the needles are pointing in opposite 

 directions, this constitutes a movement of the marked end 

 of the one towards the geographical west, and of the 

 marked end of the other towards the geographical east, 

 and this at times when the needles are under precisely 

 the same circumstances with respect to the sun's influence. 

 Now, no movement of the magnetic pole can account for 

 this, It would necessarily entail a movement of the marked 

 end of both these needles in the same geographical di- 

 rection. The consideration of this phenomenon shows us 

 that if the solar diurnal variation of the decimation is to 

 be attributed to a current, it must be one not round the 

 magnetic pole or the geographical pole, but along the mag- 

 netic meridian. But this is no[ the place for us to discuss 

 this question further at present. It would seem to be, 

 however, rather from the consideration of such phenomena 

 as this in a careful and accurate way, and the attempt 

 therefrom, by induction, to arrive at laws, that we may 

 hope to torm a theory of terrestrial magnetism, than from 

 "making an hypothesis," and taen attempting to apply it 

 to facts. J. S. 



LETTERS TO THE EDITOR 



[ Tht Editor docs not Iiold himself responsible for opinions expressed 

 by his correspondents. No notice is taken of anonymous 

 communications. ] 



Mayer and De Saussure 



In Prof. Tyndall's account of the labours ot Mayer, a para- 

 graph is devoted to the bearing of his principles upon the pheno- 

 mena of vegetable life. It suggests two points of difficulty to 

 me : — 



I. It is said that "Mayer's utterances are far from being 

 anticipated by vague statements regarding the ' stimulus ' of 

 light, or regarding coal as 'bottled sunlight.'" Nevertheless 

 the paragraph reads almost like a paraphrase of the following 

 passage from Sir John Herschel's "Outlines of A.stronomy " 

 (1833), p. 211:- 



