May 26, 1904] 



NA TURE 



75 



an allotropic modification of the element, or else to 

 \ expel some and re-arrange the remainder ; the analogy 

 ( being a spinning top which tumbles over when its 

 velocity falls below a certain critical value. [Some 

 varieties of " new star " may conceivably furnish 

 another and different kind of analogy.] 



.\ new suggestion also is made with respect to 

 Rontgen rays, viz. that they may sometimes precipitate 

 atomic disintegration and thus cause a substance to 

 emit more energy than they themselves contain. It 

 is also pointed out in a previous chapter how a shell 

 of Rontgen radiation will not disturb particles over 

 which it passes if it is below a certain thickness, 

 but if thicker than that will communicate momentum 

 to them ; and in that way a kind of modified Le Sage's 

 gravitation hypothesis is suggested, not, however, in 

 a convincing manner, but rather as one of the possi- 

 bilities that have to be discussed, and after further 

 consideration probablv abandoned. .\t the same time, 

 the hypothesis concerning radium favoured by Lord 

 Kelvin, viz. the reception of energy from a store of 

 cosmic waves and the consequent production of radio- 

 activit)', is shown to be in many respects feasible, 

 though taken all round unlikely and rather artificial. 



But the most remarkable and novel portion of the 

 book is the use made of Faraday's lines of force, and 

 the great development and importance attached to 

 ihem, in the first three chapters. Strangely enough, 

 these lines are for the first time regarded as realities ; 

 no longer as a mere map of a state of things which is 

 essentially continuous, but as an actual fibrous struc- 

 ture attributable to an electric field, and therefore 

 also to a magnetic field, and therefore also to 

 radiation. The lines of force are not only lihe 

 elastic threads which repel each other, but really 

 are such threads, though with varying thickness 

 and with their tension everywhere proportional to 

 their cross-section ; and it seems possible to think 

 of them as vortex filaments, thus reproducing in 

 ni.inv respects FitzGerald's conception of a fibrous 

 vortex ether consisting of filamental or cobweb vortices 

 interlaced in every direction (see preface to " Modern 

 \iews of Electricity," i8Sg), only these do not be- 

 come lines of force unless they are cut and terminated ; 

 the newer view regards the place where their intense 

 ends terminate as a negatively charged corpuscle or 

 electron, their wider opposite ends appearing to corre- 

 s])ond with positive electricity, the nature of Viihich, 

 however, still remains a close secret. This seems 

 lo be J. J. Thomson's view — though it is not 

 cliar that he regards the vorticity as anything 

 ir.ore than an analogy — his view is that the lines 

 of force or vortex fibres actually exist, radiating 

 (rom corpuscles, constituting electric lines of force, 

 generating magnetic fields when they move, and 

 conferring mass on the particle by reason of the 

 amount of ether entangled inextricably in each 

 filament; and he shows further how, when the fibres 

 .ire accelerated, especially when they are suddenly 

 -tarted or stopped, a much more intense local magnetic 

 field for a moment makes its appearance and rapidly 

 -.preads out as a wave of radiation, by reaction with 

 NO. 1804, VOL. 70] 



the superposed electric field, just as Larmor and others 

 have calculated, and of course in accordance with 

 Poynting's theorem. 



The whole treatment here, with simple geometrical 

 conceptions, is exceptionally interesting; and the 

 resulting view of the nature of light — that it con- 

 sists, as it were, of pulses running along the fibres 

 as along stretched strings, with constant speed be- 

 cause their tension is proportional to their mass per 

 unit length — is especially noteworthy, and is quite in 

 accordance with a guess which the genius of Faraday 

 enabled him to throw out in his famous " Thoughts 

 on Ray \"ibrations," where he says: — 



" The view which I am so bold as to put forward 

 considers therefore radiations as a high species of 

 vibration in the lines of force which are known to 

 connect particles and also masses together." 



It is clear that if this vibrating string method of 

 regarding waves of light be substantiated, a wave 

 front cannot be a continuous surface, but must be, as 

 it were, a series of isolated specks of disturbance ; sO' 

 also must a Rontgen pulse, and hence J. J. Thomson 

 is able to reconcile with theory the actually experienced 

 small ionising power of such waves, as compared with 

 what might be expected if they really and necessarily 

 encountered every atom in the field. They would, on 

 the fibrous view, be in some respects more akin to a 

 stream of kathode rays penetrating between the actual 

 corpuscular particles of matter, and only encountering 

 them occasionally, just as a comet or meteoric stone 

 only occasionally encounters a planet. 



One of the interesting features of the book — though 

 it is also contained in another volume by the same 

 author, " The Conduction of Electricity by Gases " — 

 is the summary of a re-calculation of the results of 

 Kaufmann's excellent experiments on the magnetic 

 deflection of flying particles moving with very high 

 velocity, such as can be shot off from radium. It is 

 well known that Kaufmann proved that the mass of 

 such charged bodies increases measurably as the speed 

 approaches that of light; and by comparison of his 

 results with theory he deduced, by aid of a fairly 

 plausible assumption, that the electrical portion of the 

 mass was about a quarter of the whole. 



His assumption, however, had been that the charged 

 particles behave like conducting spheres, so that the 

 lines of force would at high speeds re-distribute them- 

 selves on their surface in accordance with the calcu- 

 lations of G. F. C. Searle for metal spheres. 



J. J. Thomson, however, prefers to regard electron 

 or corpuscular particles as behaving like perfect 

 points, only points the field of which is non-e.xistent 

 within a certain small sphere surrounding each, 

 which therefore constitutes the charged surface. On 

 this view, the distribution of the lines on the 

 bounding surface of the flying particle would obey 

 a ditTerent law from that of a conducting sphere 

 at high speed, and the result of a re-calculation is 

 to make electrical mass equal to the whole mass, to 

 a remarkable degree of approximation. Thus, for 

 instance, when the speed is 2.85 x 10'" centimetres per 

 second, the observed mass is measured as 3-09 times 



