616 REPORT— 1900. 



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 alternations is high, the amount 

 of electricity that has to oscillate backwards and forwards on the guiding wires 

 is proportionately diminished, and the t'rictional waste reduced. At the terminals 

 the direct transmission from one armature of the motor to the other, across the 

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

 rubbing contacts that are unavoidable in mechanical transmission ; while the 

 perfect symmetry and reversibility 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 alternator with precise reversal of the 

 initial stages, makes this process of distribution of energy resemble the automatic 

 operations of nature rather than the imperfect material connections previously in 

 tise. 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 sethereal energy. The wonderful 

 nature of this theoretically perfect, though of course practically only api)roximate, 

 method of abolishing limitations 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 reahsed 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 experi- 

 mental 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 been largely reduced to order through 

 the employment of the high exhausnons introduced 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 conduced 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 atmosphere and in other gases by ultra-violet light, 

 the Rontgen 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 transpiration more than half a century 

 ago. This advance in experimental knowledge ot 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 ot Maxwell's 

 exposition of electric theorv, 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 pro- 

 duce the electric fields whose transformations were the main subject of the original 

 theory. 



We are thus inevitably led, in electric and sethereal 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 theoretical problems which had come clearly into view a quarter of 

 a century ago, under Maxwell's lead, whether in thp exact dynamical relations 



