NOYEMBE] 



D> 



891] 



NATURE 



:hat, with Ricardo's premiss, his" conclusion is absolutely 

 correct without any further assumption. If, on the other 

 hand, we adopt constancy of ratio (instead of constancy 

 of difference) — which was Mill's (not Ricardo's) supposi- 

 tion — then some further assumption must be made in 

 order to demonstrate that improvement in fertihty pro- 

 duces diminution of rent. In proving this point, the 

 editor uses an unnecessarily complicated piece of mathe- 

 matical reasoning. 



Without further dwelling on these defects, it is only 

 necessary to say that the explanatory footnotes are every- 

 where e.xtremely helpful, and that the frequent references 

 to Ricardo's " Letters to Malthus " will be found espe- 

 cially useful in further elucidating the great economist's 

 doctrines. W. E. J. 



OUR BOOK SHELF. 



Photographic Pastimes : a Hand-book for Amateurs. 



By Hermann Schnauss. Translated from the Second 



German Edition. (London : Iliffe and Son, 1891.) 

 -Many and varied are the effects that can be produced 

 with the aid of the camera, and the present work gives a 

 plain and popular account of the methods that have been 

 adopted in producing them. The five chapters are 

 headed, respectively — specialities, curiosities, photo- 

 graphy by peculiar arrangements, photographic optical 

 entertainments, and entertainments with photographic 

 prints. 



In carrying out the experim.ents contained under the 

 lirst two headings, amateurs will find their time fully oc- 

 cupied, while the novel effects that can be obtained will 

 afford both instruction and amusement. With reference 

 to taking pictures by moonlight, we can quite agree with 

 the author when he says that " if the moon is included 

 in the picture, its track will make a straight band of light 

 nearly half-way across the photograph, which, besides 

 the peculiar illumination of the landscape, gives a most 

 characteristic effect!' The characteristic effect, we should 

 think, would be very decided. 



An excellent and easy method of producing ghosts, 

 which may prove useful to amateurs, and which is not 

 wholly described in this book, is as follows : — The ghost 

 consists of a person completely covered over with a sheet, 

 the latter being so adjusted as to give a dim outline of 

 the head ; when in position, a short exposure of about 

 half an inch of magnesium is given : then, as soon after- 

 wards as possible, without moving anything with the 

 exception of the ghost (which now is no longer required), 

 another exposure is made, by means of a magnesium flash 

 light, of the other figures that are required for the picture. 

 In this manner excellent results have been obtained, the 

 pattern on the wall appearing through the ghost, giving it 

 quite a realistic appearance. 



In these and the remaining chapters, descriptions of 

 many novelties too numerous to mention are given, of 

 which the following may serve as types— caricature, 

 composite, and pin-hole photographs, statuary portraits, 

 kaleidoscopic and stroboscopic pictures, &c. 



Altogether, amateurs will find in this hand-book much 

 that will occupy them during the winter months, when 

 out- door photography is more or less at a standstill. 



On Surrey Hills. By a " Son of the Marshes." (Edin- 

 burgh and London : W. Blackwood and Sons, 1891.) 

 The Surrey hills are so well known that an ordinary 

 writer would find it hard to say anything fresh about them. 

 The " Son of the Marshes," however, has an exception- 

 ally good power of observation, and even familiar facts he 

 is able to present in a way that seems to give them new 



NO. 1 149. VOL. 45] 



vitality. In all his books he is especially interesting in 

 passages dealing with the habits of animals, and there 

 are many such passages in the present volume. No 

 secondhand information is offered ; the author tells us 

 only of things which he himself has had opportunities of 

 noting. Most of the chapters have already appeared in 

 Blackwood^ s Magazine, but many who read them there 

 will be glad to possess them in their present form. The 

 manuscripts of the '' Son of the Marshes " have, as usual, 

 been edited by Mr. J. A. Owen, who does not say precisely 

 how much his editorial work includes. 



Heroes of the Telegraph By J. Munro. (London : 



Religious Tract Society, 1891.) 

 The author of this book desires that it shall be regarded 

 as in some respects a sequel to his volume on " Pioneers 

 of Electricity." He begins with a short account of the 

 origin of the telegraph, and then sketches the lives and 

 principal achievements of those discoverers and inventors 

 to whom we owe the electric telegraph and the telephone 

 — Charles Wheatstone, Samuel Morse, Sir William 

 Thomson, Sir William Siemens, Fleeming Jenkin, J. P. 

 Reis, Graham Bell, Thomas Alva Edison, and D. E. 

 Hughes. In an appendix, Mr. Munro gives brief accounts 

 of various other investigators whose names are intimately 

 connected with his subject. He has a plain, straight- 

 forward style, and the book will give much pleasure to 

 young readers who take interest in the practical applica- 

 tions of science. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible 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 of iHATXJKK. 

 No notice is taken of anonymous communications.] 



The Koh-i-Nur. 



Dr. Ball, in his reply (Nature, vol. xliv. p. 592) to my 

 criticisms on his " true history " of the Koh-i-Nur, feels aggrieved 

 that I " smite him in season and out of season," and considers 

 me in the light of a partisan for doing so. I can assure him 

 that my criticisms were absolutely impersonal, as I have never, 

 to my knowledge, seen him in my life, and bear no kind of ill- 

 natured feeling towards him ; indeed, I said whatever I was 

 able honestly to do in favour of his work. But of course, where 

 I considered his arguments to be groundless or illogical, I met 

 them. If he has read into my remarks an asperity I did not 

 desire to impart to them, surely he should blame himself some- 

 what for the style of his attacks on those who went before him, 

 and of whom I have shown that they knew not less, but more, 

 of the subject than he did himself. 



I have pleasure in withdrawing my expression of an accusal! in 

 that Prof H. H. Wilson was one of those against whom Dr. 

 Ball threw out a sneer in relation to the earlier history and 

 traditions attaching to the Koh-i-Nur. I supposed that, as 

 he has laboured to make his knowledge of the authorities 

 on the subject complete, he would certainly have known what 

 was of common knowledge at the time as to the author- 

 ship of by far the most interesting notice ever penned on 

 the Koh-i-Nur. But that was long ago. It was that notice, 

 however, that brought me into such contact as I have had wiih 

 the subject. As a young Professor at Oxford, I had the honour 

 of knowing the great master of Sanskrit and of Indian lore : 

 and as I had been interested in Indian history I ventured to 

 approach him now some thirty-five or thirty-six years ago on 

 the subject of the values assigned by him to certain weights 

 referred to in his article. I drew his attention to Babar's vahia- 

 tion of the mishkal in ratis, and I further pointed out the prob- 

 ability of the retention by Shah Jahan of the Mogul diamond in 

 his captivity. lie received my suggestions in the kindest sp'rir 

 and offered me every help in further inquiry ; and at the Easi 

 India Company's Library he placed all the documents before me. 



I shall not weary your readers with thrashing out and ?j;ain 

 winnowing the various statements involved in this controvcisy. 



