April 1, 1897.] 



KNOWLEDGE. 



97 



come as a revelation. He said : " We are forced by the 

 phenomena to assume that there are different kinds of 

 cathode rays, whose properties merge into one another and 

 correspond to the colours of light. They differ among 

 themselves in respect of exciting phosphorescence, of 

 being absorbed, and of being deflected by a magnet." 

 This was written in 1883, yet only last year the composite 

 character of the cathode rays was announced as a new 

 discovery ! 



It was Hertz's observations on the passage of cathode 

 rays through thin layers of metal placed in vacuum tubes 

 that led to Lenard's work with tubes having an aluminium 

 window, through which tte rays could pass to the outside, 

 and afterwards resulted in Eontgen's discovery. This 

 paper of Hertz's was published in 1892, and is included 

 in the present volume. 



There are a few other papers which must be mentioned. 

 One deals with the relations between light and electricity, 

 and in it Hertz explains the evidence that light of every 

 kind is an electrical phenomenon ; then there is a paper 

 in which a scientific definition of hardness is arrived at, 

 several papers en elasticity, and a paper on the evapora- 

 tion of liquids iu vacuo ; and introducing these masterly 

 productions is Prof. Lenard's sketch of Hertz's scientific 

 development. 



We have exceeded the limits within which this review 

 ought to have been curtailed, having regard to the number 

 of other works calling for notice in these columns ; but a 

 Hertz does not often arise, and we could not in justice say 

 less of the brilliant contributions to science contained in 

 the book before us. The volume commands a place in 

 the library of every institution and individual interested 

 in physical research. It is a monument to a scientific 

 genius, and as an example of good translation it will be 

 difficult to excel. For the addition of the work to British 

 scientific literature, physicists cannot be too grateful. 



A Geographical Histonj of Mammals, By E. Lydekker, 

 B.A., F.R.S. (Cambridge University Press.) Illustrated. 

 The geographical distribution of animals is always an 

 interesting and instructive subject. Mr. Lydekker's volume 



Head of Male Mule-Deer (Cariaciis macrotis). 

 FrOiji " A Geographical Htstorij of ^animals." 



differs from others on the sime subject in several ways. 

 The distribution of fossil fo;ms las received greater 



attention, the volume deals with mammals only, and 

 needless to say the zoogeographical regions differ from 

 those o other works. It will be indeed a time of rejoic- 

 ing when all zoologists decide to adopt one system of 

 dividing the earth into zoological divisions. As the case 

 stands at present, one cannot refer to two books on the 

 subject which adopt the same regions or even the same 

 names for the regions. The general plan of Mr. Lydekker's 

 book is, after an introductory chapter, to give a detailed 

 account of each of the regions and its sub-regions. Thus, 

 after the extent and characters of the region are described, 

 an account is given of the animals inhabiting it, how they 

 probably arrived, and how they differ from or resemble the 

 animals of other regions ; the palmontology of the region 

 is then treated of at some length. The book is undoubtedly 

 a good one for the student, although we are inclined to 

 think that the author has, like a good host, offered more 

 than enough to satiate the most ambitious. 



SHORT NOTICES. 



Lisi of Private Libraries. T'ol. I. — TAe United States and 

 Canada. (Leipzig: Cf. Hedeler.) This is the first Tolume of an 

 interesting project for bringing together brief descriptions of the 

 more important private collections of books, manuscripts, autographs, 

 prints, portraits, etc , as well as fine bindings. This Tolume deals 

 with the United States and Canada, and is intended to be followed 

 by one dealing with Grreat Britain. The owners' names appear in 

 alphabetical order, and the description is set out in English, French, 

 and German, side by side. This alphabetical list is followed by an 

 index to towns, and also a subject index. 



The J^arth and its Story : a I'irst BooTc of G-eoIoqtf. By Ange'o 

 Heilprin. (Boston : Silver, Burdett, & Co. London : Gay & Bird.) 

 5s. Illugtrated. Admirably conceived, clearly and lucidly written, 

 with a good index, and sixty -four n.ost informing illustrations, this 

 is an excellent pupular maiiual on the story of the ages. The author 

 claims for his illustrations that they are mainly reproductions from 

 photographs taken in the field, and they certainly form most interest- 

 ing accompaniments to the text. 



The Literature of Music. By James E. Matthew. (Elliot Stock.) 

 This is a new- volume of the favourite Book-Lovers' Library, and the 

 autlior is avowedly an enthusiast in liis subject. The attempt to cover 

 so much ground iu so limited a s^iace has rendered the task a difficult 

 one, and if the result is rather a catalogue than a narration it is 

 largely due to the exigencies of space. Much valuable information 

 on the literature of anc ent and modern music and musical instru- 

 ments, together with its histories, dictionaries, and bibliography, is 

 brought together, the whole being sujiplemented by au index. 



Greentpood's Library Year Book. Edited by Thomas Greenwood. 

 (Cassell & Co.) This exeelUmt annual presents a lucid record of 

 goodly work, and iMr. Greenwood is to be congratulated upon tlie 

 phenomenal success which has attended his efforts in the public 

 library movement. 



The .Art of Projection and Complete Mayic Lantern Manual. By 

 an Expert. (E. A. Beckett, 111, Kingsland Boad, N.E.) Illustrated. 

 Ss. 6d. To those who need assistance in the management of the 

 lantern, and reliable information respecting the many accessory pieces 

 of apparatus used in conjunction therewith, we can recommend this 

 book. It is profusely illustrated with figures that plainly indicate 

 the correct methods for obtaining desired results, tables of ready 

 reference for showing the relations between lantern and disc with 

 object-glasses of all ordinary focal lengths, together with carefully 

 detailed instructions for performing experiments in cells, etc., and 

 projecting the en'arged images on the screen. 



Induction Coils and Coil-Making. By F. C. Allsop. (Spon.) 

 Illustrated. A large portion of this book has already appeared, in 

 article form, in the Enylish Mechanic. Mr. Allsop is, of course, a 

 manufacturing electrician, and his work, as far as technical details are 

 concerned, may be relied tipun. The book, however, is not merely a 

 series of lessons on the construction of coils, and batteries for woi'king 

 coils, but it also includes a pretty thorough summary of the literature 

 on these subjects. There are, moreover, chapters on the method of 

 obtaining photographs of electric discharges, and a very understandable 

 description of the X-ray apparatus, together with a simple means of 

 obtaining photographs. A photograph of the author's hand by means 

 of a four-inch coil, with two minutes' exposure, is here reproduced, 

 and it is a very good exam]ile of what may be done by means of 

 home-made appliances. 



