NA TURE 



[May 17, 1S94 



in an unsuccessful attempt to wrestle with the novelties 

 submitted to consideration. The only possible con- 

 solation or reward is the thought that a brief notice may 

 prevent others from a similar distress and dissatisfac- 

 tion. To say that the author does not accept the first 

 law of motion, will perhaps serve to indicate the kind of 

 man with whom we have to deal. After this one will be 

 prepared to believe that any amount of curiosities and 

 world-worn paradoxes will be met with in this collection 

 of some two hundred quarto pages. 



The feature, however, which distinguishes this pro- 

 duction from all other works of the same character is 

 the numerous suns which the author is obliged to intro- 

 duce in order to explain the motions of the earth and 

 moon. For those who are so benighted as to accept the 

 gravitational theory, as developed by Newton and his 

 school, one sun suffices ; but the new Principia requires 

 at least four. First, we have a central sun occupying 

 " the eccentric centre of an ideal sphere." This phrase 

 is hard to understand. It is suggested that it may mean 

 that an imaginary sphere rotates about a point not its 

 centre. Round this " ideal sphere" we have a so-called 

 polar sun, circulating with its cortege of solar bodies 

 and their satellites. This sun is called a polar sun 

 because it revolves in a plane approximately parallel to 

 the axis of the earth ; but in what the peculiar necessity 

 of its creation consists, we have failed to fathom with 

 distinctness, and fear to misrepresent the ingenious 

 author. On the surface of this ideal sphere another 

 sun, called the equatorial, also revolves, this time from 

 west to east, in a " mean equatorial plane. ' These three 

 suns are necessarily made to be non-luminous bodies, 

 only recognisable by the effects their " eccentric 

 attractions and orbital revolutions " exercise on the 

 earth and moon. Finally we have the visible sun. Of 

 these four, the central sun is the master-key of the whole 

 system, from which energy radiates in every direction, 

 upholds all the members of the system, while simul- 

 taneously holding them apart. .'Vnd any one who is at 

 all accustomed to this kind of literature will conclude, 

 without any further warning, that electricity is the energy 

 invoked to sustain this system. It would have been 

 distinctly disappointing not to have had electricity 

 introduced as the mainstay. 



Those who wish to see how this complication can be 

 made to explain the precession of the equinoxes, the 

 motion of the lunar nodes and apsides, nay, the pre- 

 dominance of land and water in the northern and 

 southern hemispheres of the earth respectively, and 

 many other strange thingf, must be referred to the book 

 itself. There is, m fact, only one sentence in the book 

 with which we can cordially and entirely agree, and that 

 is the first " Who," says the author, " Who will believe 

 the theory of astronomical motion set forth in the 

 following pages ." Not the astronomers, certainly." We 

 venture to assure him that he is perfectly correct in this 

 conjecture. W. E. P. 



A Manual nf the Geology of India. .Second edition. 

 Revised and largely re-written by R. D. Oldham, 

 AR..S.M , (Calcutta: Geological Survey Office. Lon- 

 don: Trubner and Co., 1893.) 

 The first edition of this book has been out of print for 

 some years; meanwhile, Indian geology has greatly 

 a!--^' • • ' o that a revised and extended issue, bringing 

 t : line witli the new results of the Geological 



'"1'/ been needed. Few are more capable of 

 <\ ting and revision better than Mr. (Jld- 



h 1 .1 wide and varied experience of survey 



work mi: s acquaintance with the literature 



pertaining ct is evidenced by the " Uibliography 



of Indian compiled by him in 18S8. Mr. 



Uldham h.i iltcrcd the arrangement of the book. 



The origmal cJitiu:i consisted of a series of descriptions 



N'J. I 28 I, VOL. 50] 



of separate districts; but in the present volume the rocks 

 are described in chronological order. All references to 

 economic geology are excluded, being relegated to the 

 works specially devoted to it, whde this deals with strati- 

 graphical and structural geology. In the detailed table 

 of contents, the excellent plan has been followed of indi- 

 cating by a ditterent type the matter which is new or 

 entirely re-written in the present edition. A glance at 

 this shows at once that Mr. Oldham has produced almost 

 a new book. Especially interesting is the chapter on the 

 " Homotaxis of the Gondw.ina System." Most geologists 

 will remember the bitter controversy that once raged 

 over the age of this system, but which has now died out. 

 Mr. Oldham has made a detailed study of the rock- 

 groups of the Gondwana system, and has compared them 

 with their representatives in Australia and .A.frici. He 

 has thus been able to show the relation of the Upper 

 Palicozoic and Lower. Me-;ozoic rocks of India, . Africa, 

 and Australia to those of Europe. The two last chapters 

 in the book are entirely new. One deals with the age and 

 origin of the H imalayas, and the other with the geological 

 history of the Indian peninsula. In both of these a 

 number of important questions are discussed in a 

 scientific manner. Wherever Mr. Oldham has inter- 

 polated new matter, he has done it well. Unlike many 

 other revisers, therelore, he has produced a restoration 

 which really improves the old structure. The result is 

 that the manual is once more the standard work on 

 the present state of knowledge of the geology of India. 



LETTERS TO THE EDITOR. 



\The Editor Joes not hold himself rtsponsihU for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part 0/NATUR8. 

 No notice is taken of anonymous communications.] 



The Weight of the Earth. 



In a letter in this week's Nature, signed " The Reviewer," 

 the writer does not notice that in ihe English l.inguage, and in 

 all legal and common usages of it, including that of all scientific 

 men in speaking of their weii;liings l>y ordinary balances, 

 -Meights mean masses. Tlie fact that the weijjht of the earth 

 is 614 X IO-' tons is as clear as that the weight of a parcel of 

 tea is 3 lb. It is the heaviness of a weight or mass that is a 

 property accidental to its position, being less at the equator, 

 greater at the poles, and nothing at the earth's centre. I have 

 never yet heard a " box of wcighlb " called a box of misses. I 

 don't believe even "The Reviewer" calls it a box of masses. 

 If carried to the centre of the earth it is still a box of weights, 

 though the heaviness of the weights is zero. 



The word " weight " is often used to denote the heaviness of 

 a weight or mass. No dictum, either of "The Reviewer" or 

 of myself can eliminate this ambiguity from the ICiiglish language. 

 Hut scienlilic men may grcitly diminish the inconvenience of it, 

 and may even tend to eliminate it altogether, if they persistently 

 use the woid "heaviness" when they mean heaviness. 



May 12. R. 



"The Reviewur" makes a number of statements which he 

 does not slop to prove; a', for instance, when he says lint 

 " the weight of a body would be pr.ictically nothing if the body 

 was removed to a few million miles fr.iin the earth." liut an 

 appeal to experiment will show that the weight is unaltered. 

 To fix the ideas, consider an astronomical or .istrological chart, 

 in which the earth is at the centre of a Zodiacal circle. Now, il 

 a IOC-ton gun is weighed in the .scales of Libra, the weights 

 required for equilibrium, as given by the lumps of metal in the 

 other scale pan, will amount to exactly too tons ; so that the 

 weight of too tons at the distance of the Zodiacal circle, or at 

 any other distance, is exactly 100 tons. 



Hut if "The Reviewer" takes a ball of the mathematician's 

 imaginary fine, weightless siring, which he lets down from 

 Libra to the surface of the earth, to the end of which weights 

 can be attached, so as to equilibrate the 100 ton gun at the di»- 



