450 



NA TURE 



[September 6, 1900 



fields of force. His analysis of the facts of magnetic influence, 

 and incidentally of the points in which it differs from electric 

 influence, is virtually the one which Faraday re-introduced, A 

 cardinal advance was achieved, at a time when the Copernican 

 Astronomy had still largely to make its way, by assigning the 

 behaviour of the compass and the dip needle to the fact that the 

 earth itself is a great magnet, by whose field of influence they 

 are controlled. His book passed through many editions on the 

 Continent within forty years ; it won the high praise of Galileo. 

 Gilbert has been called " the father of modern electricity" by 

 Priestley, and " the Galileo of magnetism " by Poggendorff. 



When the British Association last met at Bradford in 1873 

 the modern theory which largely reverts to Gilbert's way of 

 formulation, and refers electric and magnetic phenomena to the 

 activity of the aether instead of attractions at a distance, was of 

 recent growch ; it had received its classical exposition only two 

 years before by the publication of Clerk Maxwell's treatise. 

 The new doctrine was already widely received in England on 

 its own independent merits. On the Continent it was engaging 

 the strenuous attention of Helmholtz, whose series of memoirs, 

 deeply probing the new ideas in their relation to the prevalent 

 and fairly successful theories of direct action across space, had 

 begun to appear in 1870. During many years the search for 

 crucial experiments that would go beyond the results equally 

 explained by both views met with small success ; it was not 

 until 1887 that Hertz, by the discovery of the asthereal radiation 

 of long wave-length emitted from electric oscillators, verified 

 the hypothesis of Faraday and Maxwell and initiated a new era 

 . in the practical development of physical science. The experi- 

 mental field thus opened up was soon fully occupied both in 

 this country and abroad ; and the borderland between the 

 sciences of optics and electricity is now being rapidly explored. 

 The extension of experimental knowledge was simultaneous 

 with increased attention to directness of explanation ; the ex- 

 positions of Heaviside and Hertz and other writers fixed atten- 

 tion, in a manner already briefly exemplified by Maxwell him- 

 self, on the inherent simplicity of the completed rethereal 

 scheme, when once the theoretical scaffolding employed in its 

 construction and dynamical consolidation is removed ; while 

 Poynting's beautiful corollary specifying the path of the trans- 

 mission of energy through the aether has brought the theory into 

 simple relations with the applications of electrodynamics. 



Equally striking has been the great mastery obtained during 

 the, last twenty years over the practical manipulation of electric 

 power. The installation of electric wires as the nerves connect- 

 ing different regions of the earih had attained the rank of ac- 

 complished fact so long ago as 1857, when the first Atlantic 

 cable was laid. It was largely the theoretical and practical 

 difficulties, many of them unforeseen, encountered in carrying 

 that great undertaking to a successful issue, that necessitated 

 the elaboration by Lord Kelvin and his coadjutors of convenient 

 methods and instruments for the exact measurement of electric 

 quantities, and thus prepared the foundation for the more recent 

 practical developments in other directions. On the other hand, 

 the methods of theoretical explanation have been in turn im- 

 proved and simplified through the new ways of considering the 

 phenomena which have been evolved in the course of practical 

 advances on a large scale, such as the improvement of dynamo 

 armatures, the conception and utilisation of magnetic circuits, 

 and the transmission of power by alternating currents. In our 

 lime the relations of civilised life have been already perhaps more 

 profoundly altered than ever before, owing to the establishment 

 of practically instantaneous electric communication between all 

 parts of the world. The employment of the same subtle agency 

 is now rapidly superseding the artificial reciprocating engines 

 and other contrivances for the manipulation of mechanical power 

 that were introduced with the employment of steam. The 

 possibilities of transmitting power to great distances at enormous 

 tension, and therefore with very slight waste, along lines merely 

 suspended in the air, are being practically realised ; and the 

 advantages thence derived are increased manifold by the almost 

 automatic manner in which the electric power can be transformed 

 into mechanical rotation at the very point where it is desired to 

 apply it. The energy is transmitted at such lightning speed that 

 at a given instant only an exceedingly minute portion of it is in 

 actual transit. When the tension of the aliernations is high, 

 the amount of electricity that has to oscillate backwards and 

 forwards on the guiding wires is proportionately diminished, and 

 the frictional waste reduced. At the terminals the direct trans- 

 mission from one armature of the motor to the other, across the 



NO. 1610, VOL. 62] 



intervening empty space, at once takes us beyond the province of 

 the pushing and rubbing contacts that are unavoidable in 

 mechanical transrriission ; while the perfect symmetry and re- 

 versibility of the arrangement by which power is delivered from 

 a rotatory alternator at one end, guided by the wires to another 

 place many miles away, where it is absorbed by another alter- 

 nator with precise reversal of the initial stages, makes this 

 process of distribution of energy resemble the automatic opera- 

 tions of nature rather than the imperfect material connections 

 previously in use. We are here dealing primarily with the 

 flawless continuous medium which is the transmitter of radiant 

 energy across the celestial spaces ; the part played by the 

 coarsely constituted material conductor is only that of a more or 

 less imperfect guide which directs the current of aeihereal energy. 

 The wonderful nature of this theoretically perfect, though of 

 course practically only approximate, methodof abolishing limita- 

 tions of locality with regard to mechanical power is not diminished 

 by the circumstance that its principle must have been in some 

 manner present to the mind of the first person who fully realised 

 the character of the reversibility of a gramme armature. 



In theoretical knowledge a new domain, to which the theory 

 as expounded twenty years ago had little to say, has recently 

 been acquired through the experimental scrutiny of the electric 

 discharge in rarefied gaseous media. The very varied electric 

 phenomena of vacuum tubes, whose electrolytic character was 

 first practically established by Schuster, have l^een largely reduced 

 to order through the employment of the high exhaustions intro- 

 duced and first utilised by Crookes. Their study under these 

 circumstances, in which the material molecules are so sparsely 

 distributed as but rarely to interfere with each other, has con- 

 duced to enlarged knowledge and verification of the fundamental 

 relations in which the individual molecules stand to all electric 

 phenomena, culminating recently in the actual determination, by 

 J. J. Thomson and others following in his track, of the masses 

 and velocities of the particles that carry the electric discharge 

 across the exhausted space. The recent investigations of the 

 circumstances of the electric dissociation produced in the atmo- 

 sphere and in other gases by ultra-violet light, the Rontgeri 

 radiation, and other agencies, constitute one of the most striking 

 developments in experimental molecular physics since Graham 

 determined the molecular relations of gaseous diffusion and trans- 

 piration more than half a century ago. This advance in experi- 

 mental knowledge of molecular phenomena, assisted by the 

 discovery of the precise and rational effect of magnetism on the 

 spectrum, has brought into prominence a modification or rather 

 development of Maxwell's exposition of electric theory, which 

 was dictated primarily by the requirements of the abstract theory 

 itself; the atoms or ions are now definitely introduced as the 

 carriers of those electric charges which interact across the aether, 

 and so produce the electric fields whose transformations were the 

 main subject of the original theory. 



We are thus inevitably led, in electric and fethereal theory, as 

 in the chemistry and dynamics of the gaseous state which is the 

 department of abstract physics next in order of simplicity, to the 

 consideration of the individual molecules of matter. The theo- 

 retical problems which had come clearly into view a quarter 

 of a century ago, under Maxwell's lead, whether in the exact 

 dynamical relations of cethereal transmission or in the more 

 fortuitous domain of the statistics of interacting molecules, are 

 those around which attention is still mainly concentrated ; but 

 as the result of the progress in each, they are now tending 

 towards consolidation into one subject. I propose — leaving 

 further review of the scientific aspect of the recent enormous 

 development of the applications of physical science for hands 

 more competent to deal with the practical side of that subject — 

 to offer some remarks on the scope and validity of this molecular 

 order of ideas, to which the trend of physical explanation and 

 development is now setting in so pronounced a manner. 



If it is necessary to offer an apology for detaining the attention 

 of the Section on so abstract a topic, I can plead its intrinsic 

 philosophical importance. The hesitation so long felt on the 

 Continent in regard to discarding the highly-developed theories 

 which analysed all physical actions into direct attractions 

 between the separate elements of the bodies concerned, in favour 

 of a new method in which our ideas are carried into regions 

 deeper than the phenomena, has now given place to eager dis- 

 cussion of the potentialities of the new standpoint. There has 

 even appeared a disposition to consider that the Newtonian 

 dynamical principles, which have formed the basis of physical 

 explanation for nearly two centuries, must be replaced in these 



