Nov. 7, 1889] 



NATURE 4Z 



another generation may possibly pass away before either 

 the House of Commons or even Ministers are sufficiently 

 instructed in science to recognize fully their responsibility 

 in this direction. 



Whatever, then, the future may bring, the last twenty 

 years have been characterized by progress both steady 

 and rapid. The tide flows on with no sign of check, 

 and we accept the success of Nature in no spirit of 

 self-gratulation, but as a straw by which the speed of the 

 current may be gauged. 



MODERN VIEWS OF ELECTRICITY. 

 ^Todern Views of ElectHcity. By Oliver J. Lodge, D.Sc, 



LL.D, F.R.S. (London: Macmillan and Co., 1889.) 

 T N this interesting book Prof. Lodge gives a very lively 

 -»- and graphic account of many of the most recent 

 speculations about the nature of electrical phenomena. 

 A work with this object was urgently needed, as" the 

 method of regarding these phenomena given in popular 

 treatises on electricity is totally different from that used 

 by those engaged in developing the subject. 



The attention called by Faraday and Maxwell to the 

 effects produced by and in the medium separating electri- 

 fied bodies has had the effect of diverting attention from 

 the condition of the charged bodies in the electric field 

 to that of the medium separating them, and it is perhaps 

 open to question whether this of late years has not been 

 too much the case. To explain the effects observed in 

 the electric field we should require to know the condition 

 not only of the ether, but also of the conductors and in- 

 sulators present in it ; just as a complete theory of light 

 would include the state of the luminous bodies as well as 

 of the ether transmitting the radiations excited by them. 

 Since matter is more amenable to experiment than the 

 ether, it seems most probable that we shall first gain an 

 insight into the nature of electricity from a study of 

 those cases where matter seems to play the chief part — 

 such as in the electric discharge through gases, and 

 the phenomena of electrolysis — rather than from specula- 

 tions, however interesting, as to what takes place in the 

 ether when it is transmitting electrical vibrations. Prof. 

 Lodge, however, in the work under consideration, devotes 

 most of his space to the consideration of the ether. In 

 his preface he says, " Few things in physical science 

 appear to me more certain than that what has so long 

 been called electricity is a form, or rather a mode, of 

 manifestation of the ether ; " and he proceeds to give 

 precision to this somewhat vague statement by developing 

 a theory that electricity is a fluid, and a constituent of a 

 very complex ether. In the first few chapters he sup- 

 poses that all insulators, including the ether, have a 

 cellular structure the cells being filled with a fluid which 

 is electricity, and which is not able to get from one cell 

 to another unless the walls of the cells are broken down ; 

 in conductors, however, there are channels between the 

 cells, so that the electricity is able to flow more or less 

 freely through them. A flow of this fluid is an electric 

 current. But if this is the case, anything which sets the 

 ether in motion will produce an electric current. Now, 

 Fizeau's experiments show that moving bodies carry the 

 ether with them to an extent depending on their index 



of refraction ; so that a disk made of glass or other 

 refracting substance, if set in rapid rotation about an 

 axis through its centre, and at right angles to its plane, 

 ought to act as if currents were circulating in the disk, 

 and produce a magnetic field around it. In order to 

 avoid the allied difficulty that nothing has ever been 

 observed which indicates that a magnet or a current 

 flowing through a coil possesses gyroscopic properties, 

 Prof. Lodge assumes, in subsequent chapters, that the 

 fluid in the cells of the ether is a mixture of two fluids, 

 and that these two fluids are positive and negative elec- 

 tricity : and that, in order to exhibit any electrical effect, 

 the compound fluid has first to be decomposed into posi- 

 tive and negative electricity by the application of an 

 electromotive force. A current of electricity, on this view, 

 consists of the flow of equal quantities of positive and 

 negative electricity in opposite directions. Thus this, the 

 most " modern view of electricity," is in its most im- 

 portant features almost identical with the old two-fluid 

 theory published by Symmer in 1759. We confess we do 

 not think the theory in its present form advances the 

 science of electricity much : it does not suggest new phe- 

 nomena, nor does it lend itself readily to explain the 

 action of matter in modifying electrical phenomena; it 

 demands, too, a very artificial ether. It would seem that 

 the first steps required to make a theory of this kind a 

 real advance on the old two-fluid theory would be the dis- 

 covery of a structure for the ether, which would possess 

 the same kind of properties as the mixture of the two 

 electricities on that theory. A great deal, too, is left 

 indefinite in the theory : thus, for example, we are not 

 told whether for a given current these streams are moving 

 slowly or with prodigious velocities. In fact, there is 

 throughout the book rather a want of definite conclusions, 

 and this is rather hidden by the vigorous style in which 

 Prof Lodge writes : he develops his ideas in such an 

 enthusiastic and interesting way that on the first reading 

 they seem to be a good deal more definite than they prove 

 to be on calmer reflection. 



But whatever may be thought of Prof Lodge's theory 

 of electricity, there can be, we think, no two opinions of 

 the value of the numerous models illustrating the proper- 

 ties of electrical systems which he has invented. These 

 must prove of the greatest assistance in enabling the 

 student to gain a clear and vivid idea of electrical pro- 

 cesses, and ought to be largely employed by all teachers 

 of electricity. 



In a work dealing so briefly with such a multitude of 

 different and difficult subjects it is natural that there 

 should be many statements to which exception might be 

 taken. Prof Lodge disarms criticism by his frank ad- 

 mission of this ; sometimes, also, by an amusing vagueness 

 of statement : thus, on p. 206, in speaking of the condi- 

 tion of the ether in>icie a strongly-magnetizable substance, 

 he says : " Perhaps it is that the atoms themselves revolve 

 with the electricity ; perhaps it is something quite differ- 

 ent." There are, however, some statements of a less 

 theoretical kind which seem to us likely to mislead the 

 student. Thus it is stated that the amount of the Peltier 

 effect shows that the difference of potential between zinc 

 and copper is only a few micro-volts. The Peltier effect, 

 however, without further assumption, cannot tell us any- 

 thing about the absolute magnitude of the difference of 



