October i6, 1890] 



NA TURE 



591 



■c>r\ acetylene, in which, by the way, there occurs the very 

 objectionable expression "two volumes of carbon" in 

 reference to the composition of the gas. The statement 

 that " nitric acid is largely used in the manufacture of 

 sulphuric acid'"' needs qualification, especially as we are 

 t old that " sulphuric acid is largely employed in the 

 i)repa ration of . . . nitric acid." But, on the whole, the 

 manual is one that deserves recommendation, and will be j 

 valued by those for whose use it has been written. 



We would suggest that, in the future editions that will ' 

 doubtless be called for, "choke" or "after-damp" be not 

 described as carbon dioxide, because the amount of ' 

 carbon dioxide in it is very small comp:ired with the 

 nitrogen present ; and we do not think that the examiners | 

 at South Kensington would harshly judge any student ; 

 who corrected the current notion. And if the engraver i 

 of the illustrations had photographs of the apparatus i 

 supplied him, or, better still, if the blocks could be i 

 prepared mechanically from such photographs, the figures | 

 would have an appearance of genuineness which at present [ 

 many of them lack. It is better to represent the apparatus 

 used than the operation in progress, and then one avoids j 

 such unnecessary and unwise conventionalities as appear 

 in the attempt to illustrate a brilliant combustion in a 

 glass jar. 



Arithmetical Cheviistry. Part I. By C. J. Woodward, 

 B Sc. New Edition. (London : Simpkin, Marshall, and 

 Co., 1890.) 



In the study of chemistry there is a certain amount of 

 arithmetical work which the elementary student must 

 master as he progresses, and this used to be generally 

 considered as the part in which the young pupil was 

 most likely to fail. But now it is different, and we fear 

 that there is rather a danger of too much stress being 

 laid upon arithmetical exercises. In the volume before 

 us the author proceeds by easy stages, explaining the 

 various subjects dealt with in a sound and simple 

 manner. We hope for the student's sake that it is 

 intended for the teacher to select from the numerous 

 exercises set. At the end of the volume there are " the 

 whole of the questions in arithmetical chemistry and 

 chemical philosophy," selected from the examination 

 papers of five different examining bodies, for the years 

 1886 to 1889 inclusive. These will doubtless be useful to 

 the teacher if used with discretion enough to prevent his 

 students from imagining that chemistry is a branch of 

 arithmetic. 



Air-Analysis : with an Appendix on Illuminating Gas. 

 By J. Alfred Wanklyn and W. J. Cooper. (London : j 

 Kegan Paul, Trench, Triibner, and Co., Ltd., 1890.) j 



This small volume of ninety pages is a practical guide I 

 to air-analysis, especially for sanitary purposes. The ; 

 directions are plam, and multiplication of methods is J 

 avoided. Hempel's apparatus is employed. For the 1 

 estimation of oxygen, nitric oxide is advised, and it is i 

 pointed out that as an excess of the gas is used it need j 

 not be pure. The authors state that, in their hands, this 

 method has proved very accurate, and they give experi- i 

 mental results showing that it is to be preferred to j 

 alkahne pyrogallol or explosion with hydrogen. Direc- ; 

 tions for these latter methods are, however, included. | 

 The estimation of small quantities of carbonic oxide is 

 performed by absorption in a cuprous chloride solution, 

 with subsequent elimination and measurement of the 

 gas. The analysis of coal-gas is dealt with in the 

 appendix, and the volume concludes with some useful 

 tables. As an addition to the treatises on special 

 branches of analysis written by Mr. Wanklyn, either solely 

 or jointly, this volume will be welcomed by analysts and 

 students. 



NO. 1094, VOL. 42] 



Fresh-water Aquaria : their Construction, Arrangement, 

 and Management. By Rev. Gregory C. Bateman. 

 (London: L. Upcott Gill, 1890.) 

 Mr. Bateman says that he has always been fond of 

 natural history, and that when he was a boy he looked 

 forward with pleasure to the prospect of having an 

 aquarium of his own. When this delight was experi- 

 enced, he found that it had many drawbacks. These 

 were due to the fact that he did not know how to manage 

 his treasure. He bought or borrowed books on the 

 subject, but was not able to obtain all the information he 

 required. Then he tried to find out by experiment what 

 he could not learn by reading ; and as most of his at- 

 tempts were in the end successful, he resolved that he 

 would write such a book as he himself had wished for 

 when he was making his " first blunders in aquarium 

 matters." The present volume is the result of this de- 

 cision, and there can be no doubt that it will be very 

 cordially welcomed by many students who want just such 

 information as the author has brought together. He 

 writes simply, clearly, and practically, and no one who 

 reads with moderate care what he has to say will find 

 much difficulty in complying with the rules he lays down. 

 He gives, also, interesting details as to the best water- 

 plants and live stock to be kept, how and where they are 

 to be obtained, and how they are to be maintained in 

 health. The volume includes many illustrations. 



Scenes and Stories of the North of Scotland. By John 

 Sinclair. (Edinburgh : James Thin. London : Simp- 

 kin, Marshall, and Co. 1890.) 



Mr. Sinclair is an intelligent and lively writer, and has 

 produced a book which may be read with pleasure by 

 persons who have visited, or think of visiting, the scenes 

 he describes. The work is not, in the strict sense, scien- 

 tific ; but it includes many passages which are, to a cer- 

 tain extent, of scientific interest. The subjects are : Loch 

 Duich, Ross-shire ; the Black Rock, Ross-shire ; the 

 Island of Lewis ; Assynt, in Sutherland ; the Caithness 

 coast ; the town of Thurso ; and the Shetland Islands. 

 Here is ample scope for fresh observation and bright de- 

 scription ; and the author has generally made good use 

 of his opportunities. It is to be regretted, however, that 

 he did not, before writing of the Island of Lewis, make 

 himself acquainted with what trustworthy archaeologists 

 have said about the great prehistoric monument at Caller- 

 nish. " There is little doubt," he asserts, " that these 

 standing stones are a monument of the ancient Druids." 

 There is not a shred of evidence that the D'-uids had 

 anything whatever to do either with these or with any 

 other " standing stones." 



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 Nature. 

 No notice is taken of anonymous communications. '\ 



The Discharge of Electricity through Gases. 



On returning from abroad I find that Prof. [. J. Thomson 

 has written to you to complain about a passage in my Bakerian 

 Lecture, and I should like to say a few words in explanation. I 

 am sorry if I have said anything that would seem unfair to Prof. 

 Thomson, but I have re-read his paper, and confess that my 

 difficulties have not been cleared away. 



I i-hall be glad to be allowed to enter somewhat fully into 

 the objection raised by Prof. Thomson to my remarks, as, in- 

 dependently of any personal question, this may help to clear up 

 some disputed matters. The point at issue between Prof. 

 Thomson and myself is, whether the Clausius- Williamson dis- 

 sociation hypothesis forms an essential portion of the views on 



