264 



NA TURE 



yjuly 22, 1880 



The book makes no claim to be a complete treatise, but 

 rather to deal with those branches of the science with 

 which the author is best acquainted, one might almost 

 say, those parts at which he has himself worked, either 

 originally or by way of verifying the work of others. As 

 might be expected from such a scheme, the descriptions 

 of apparatus and phenomena are admirable, but, unfor- 

 tunately, the theoretical explanations, intended to give 

 the book more or less the character of a systematic 

 treatise, are neither clear nor accurate. So early as 

 page 2 we read : " It is found that if equal quantities of 

 the electricity of glass and the electricity of sealing-wax 

 be added together they neutralise each other." But this 

 is not preceded by any explanation of what is meant 

 by equal quantities of the electricities of glass and sealing- 

 wax. If the sentence had been cast as a definition, it 

 would have been comprehensible. On page 20 there is an 

 extraordinary illustration of the medium supposed to 

 transmit electrostatic forces : — 



"The transmission of strain may be very beautifully 

 seen at any railway-station when shunting is going on, if 

 a train of carriages is being pushed by an engine which 

 happens, instead of giving a steady pressure, to strike a 

 slight blow on the carriage nearest to it. The furthest 

 carriage does not move at once, but the buffer springs are 

 compressed — that is, the first carriage is for an instant 

 strained by having its total length shortened by some 

 inches. It instantly recovers from this strain by the ex- 

 pansion of the springs ; but as it cannot expand towards 

 the engine, it expands away from it, and transmits the 

 strain to the next carriage by compressing its buffer- 

 springs, and the process is repeated all the way from the 

 engine to the carriage furthest from it." 



This buffer experiment is an illustration of wave-motion, 

 an idea we do not need in any theory of electrostatics. 

 On page 23 there is a popular explanation from the pen 

 of Prof. Ayrton of the easy discharge of electricity from 

 points ; this remarkable explanation does not in any way 

 depend on the greater electric surface density at and near 

 a point, and it suggests that the force near a conductor is 

 not normal to its surface. It is unnecessary to pursue 

 this criticism further ; we have said enough to show that 

 Mr. Gordon's strength does not lie in the systematic 

 exposition of electrical theory. 



The book is divided into four parts — Electrostatics, 

 Magnetism, Electrokinetics, and Electro-optics. In the 

 third part is included all the phenomena of current 

 electricity. This is an unsatisfactory classification. 

 Electrokinetics should be' confined to those phenomena 

 of current electricity which involve the kinetic energy of 

 current, such as electromagnetism and electromagnetic 

 induction. The author would have been wiser to have 

 followed the arrangement of Maxwell, and have classed 

 the steady flow of electricity in conductors at rest rather 

 with electrostatics than electrokinetics. Adams's experi- 

 ments on equipotential lines and surfaces in conductors 

 are interpolated between diamagnetism and the induction 

 coil ; they are, of course, naturally a part of the theory of 

 electrical resistance, and have no near connection with 

 the chapter preceding or following. 



Great care has been bestowed on the illustration of the 

 work. We know of no book on electricity so beautifully 

 illustrated. Nor are the pictures merely pictures. They 

 show well the details of apparatus ; often, too, some 



leading dimensions are given when perspective does not 

 admit of a scale. We would recommend this practice to 

 all writers on science. It is a great help to the imagin- 

 ation to know how large a thing is, and better that this 

 information should be upon the picture than in the text 

 only. 



In the construction of this book the freest use has been 

 made of the scissors, whole pages being quotations. This 

 is both wise and modest, for when the original works of 

 the man who discovered and stated a fact are suitable 

 for a treatise, there can be no use in paraphrasing them. 

 .Some of the chapters are excellent analyses of the several 

 investigations which have been made into the subjects of 

 which they treat. This is notably the case with the 

 chapter on " Specific Inductive Capacity." When Mr. 

 Gordon has occasion to prepare a new edition he will do 

 well to expand where he is strongest, to omit as far as 

 possible systematic exposition, but to make each chapter 

 a history to which the reader may refer wdth confidence 

 that he will there find a clear account of every original 

 experiment, English or foreign, that has been tried in 

 that department. The value of such a work would be 

 inestimable. 



STRATIGRAPHICAL GEOLOGY 

 Lethcea geognostica, oder BescJuxibting tind Abbilding 

 der fur die Gehirgs-Foniiationen bescichnendsten Ver- 

 steincrungen. Herausgegeben von einer Vereinigung 

 von Palaontologen. I. Theil : Lcthaa palceosoica, you 

 Ferd. Roemer. Textband : Erste Lieferung. Pp. 324. 

 (Stuttgart, 1 8S0.) 



THE study of fossils may be approached from two 

 distinct points of view : wc may regard them as 

 furnishing us with additional illustrations of the diversi- 

 ties of form and structure in the animal and vegetable 

 kingdoms, or we may study them as making their appear- 

 ance in a certain definite order, and thus as characterising 

 particular geological formations. The former is the point 

 of view of the biologist, the latter that of the stratigraphi- 

 cal geologist. Paleontology, or the study of fossil forms, 

 must necessarily be pursued as a branch of biology, for 

 only by the study of their nearest recent analogues can 

 we hope to interpret the fragmentary and often obscure 

 relics of former inhabitants of the globe ; but, on the 

 other hand, the progress of systematic geology has been 

 bound up with the study of fossils ever since it has been 

 clearly recognised that strata can be identified by the 

 organic remains which they contain. 



German scientific literature is now being enriched by 

 the publication of tw^o very valuable works in which 

 fossils are treated of, in the one case from the stand-point 

 of the biologist, in the other from that of the stratigraphi- 

 cal geologist. The admirable treatise on palaeontology 

 b)' Zittel and Schimper gives an excellent account of th& 

 chief types of fossil plants in their relations to living 

 forms, and the work of which we have placed the title at 

 the head of the present article, promises to supply an 

 equally important contribution to stratigraphical geology. 



The title of "Lethaja Geognostica" was first employed 

 by Bronn, who between the years 1835 and 1837 published 

 a work under this name, in which he described all the 



