50 



NA TURE 



[November i8, 1897 



might expect to find \i' instead of which he finds m ; the 

 meaning, however, of this e does not seem to be given, 

 and he is left to discover for himself that this e stands 

 for the specific inductive capacity for which [i has been 

 previously employed. 



We should prefer to say that the absolute dimensions 

 of specific inductive capacity and of permeability were 

 yet unknown rather than they were " arbitrary," and we 

 do not agree with the statement that attempts to settle 

 their absolute dimensions are evidently based upon mis- 

 conceptions of the theory of dimensions. 



The statement that " for magnetic bodies as the force 

 increases /x diminishes " is generally correct, but not 

 sufficiently guarded, seeing that the very opposite is 

 the case for small forces ; and more explanation is 

 required as to the meaning, or the necessity, of the state- 

 ment : — " The variability of /x does not affect the validity 

 of Ohm's Law, which determines the distribution of the 

 laws of induction." 



The last chapter in Part ii., on the conduction in di- 

 electrics, contains some interesting work, such as that on 

 the effect of heterogeneity. 



Part iii. deals with the electromagnetic field in a lucid 

 and satisfactory manner. We feel somewhat divided in 

 our judgment regarding Mr. Webster's inability to 

 respond to Boltzmann's appeal that Maxwell's notation 

 should be followed. It will undoubtedly be somewhat 

 perplexing for the student to have to employ X, Y, Z for 

 the components of electric field intensity when he reads 

 this book, and for the components of a mechanical force 

 when he is studying Maxwell's classical treatise. But Mr. 

 Webster is an American, and the secret of the success of 

 his countrymen lies in their having gone ahead instead of 

 merely following precedent. Hence, whatever may be 

 the wrench we feel at being torn away from our time- 

 honoured notation, we must respect Mr. Webster's inde- 

 pendence in employing what he considers a better one. 



The book finishes with an excellent introduction to the 

 theory of electromagnetic waves, which deals with the 

 more important points of this subject in a clear and 

 concise manner. The statement made on page 550, that 

 the matter on the preceding seventeen pages applies only 

 to a submarine cable of infinite length, should have come 

 much earlier ; for, on reading these pages, we certainly 

 thought that the author was under the mistake of 

 imagining that the treatment applied equally well to a 

 finite cable. 



On page 536 the author pokes fun at established 

 authority by giving more than one reason why long- 

 distance telephony has not existed in England, and on 

 page 547 he sits in judgment on Mr. Heaviside in an 

 equally humorous way, although in this case the fun is 

 not intentional on the part of the author. 1 



The book is on the whole distinctly good, and any one 

 who has mastered it will possess a sound acquaintance ' 

 with the most important parts of mathematical electricity. 

 The absence of reference to experimental methods is, as , 

 stated in the preface, intentional, and, of course, no 

 practical applications of electricity are referred to. But, 

 even if this system has been followed as a protest against 

 those who forget that the practice of to-day was the theory 

 of yesterday, we would suggest that a course of " Lectures 

 NO. 1464, VOL. 57] 



on Mathematical Physics " may fitly contain explanations 

 of the physical interpretations of the equations developed 

 without running the risk of appearing to pander to the 

 needs of the electrical contractor. W. E. A. 



THE ELECTRICAL PHENOMENA OF NERVE. 

 Lectures on Physiology. (First Series.) Ott Animal 

 Electricity. By A. D. Waller, F.R.S., &c. Pp. viii 

 -J- 144. (London : Longmans, 1897.) 

 A S Fullerian Professor of Physiology, Dr. Waller has 

 ■^*- published a series of lectures on the electrical 

 properties of nerve, in which he tells us that his aim 

 has been to give "an exposition of the principal data" 

 relating to the subject. Such of these data as have been 

 derived from his own experiments have been already 

 made known by him in his published papers ; but the 

 physiological reader will find it much easier to appreciate 

 their value, now that they are placed before him in con- 

 nection with facts already known to him. A point of 

 great scientific interest in Dr. Waller's work consists in 

 the circumstance that he has adopted and strictly 

 adhered to a uniform method of " testing " the physio- 

 logical conditions of a nerve. The gratitude of the 

 reader is further excited by the perspicuity with which 

 the method itself and the first fruits of its application 

 are described, as well as by a vividness of style which 

 makes him feel as if he had been present at the 

 demonstrations. 



Dr. Waller's object is to prove that the phenomenon 

 by which a separated nerve most strikingly shows its 

 vitality — the negative variation of du Bo is-Reymond — 

 is also a measure and criterion of the physiological con- 

 dition of the nerve. For this purpose he employs an 

 automatic arrangement by which at regular intervals of a 

 minute, the appropriate " stimulus " for producing this 

 effect is applied to the nerve, at the same time that the 

 electrical " response " made by the nerve is recorded 

 photographically. The effect thus recorded — the negative 

 variation just mentioned — is the diminution of the so- 

 called nerve current, the amount of which diminution is 

 indicated by the deflections of a galvanometer connected 

 with the nerve in the usual way. Consequently, so long 

 as the strength and duration of the stimulus (a suc- 

 cession of induction currents led through the nerve at a 

 distance from the part under observation) remains con- 

 stant, the perfect uniformity of the periodical deflection 

 indicates that the state of the nerve is unaltered ; 

 and the effect of any other condition, as, e.g. acid or 

 alkaline reaction, change of temperature, &c., manifests 

 itself by augmenting or reducing the deflection. As 

 evidence that the deflection itself is a " vital " one, that 

 is, one belonging to the living nerve as such, it is shown 

 that the transient loss of function which follows the 

 action of the vapour of ether is accompanied by an 

 equally transient disappearance of the normal electrical 

 reaction of the nerve, and again, that the presence of 

 carbon dioxide in the saturated atmosphere in which the 

 nerve is placed for observation, even in the smallest 

 quantity, augments in an equally remarkable way the. 

 power of the nerve to respond to stimulation. 



