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Dr. J. Larmor. A Dynamical Theory 



■which it is only the mechanism of transmission. It is here main- 

 tained that the whole of the action between different portions of 

 matter cannot possibly be represented as transmitted by the aether 

 in that manner. It would even be a fair defence of this position to 

 claim that the onus of demonstration lies on those who assert the 

 opposite : but the material elastic medium, above mentioned, per- 

 vaded by intrinsic strain-centres, furnishes a crucial illustration. The 

 parts of that medium itself are in motion on account of the changing 

 strain ; while in addition the intrinsic strain- centres put each other 

 into motion across the medium (as vortices do across an intervening^ 

 fluid) by their mutual actions. The theory of contact action so 

 called, or elastic transmission, is not wide enough to include all this : 

 the dynamical interactions between the strain-centres are no more 

 transmitted by elastic action than the interactions between fluid 

 vortices without solid cores are transmitted by fluid pressure : though 

 in each case that agency is a necessary concomitant to the dynamical 

 effect. The really absolute thing in dynamical explanation, that on 

 which this principle of elastic transmission or contact action has 

 itself been built up by Lagrange and Green, and without which it 

 could not have assumed a precise mathematical form, is the scheme 

 of fundamental dynamical notions connecting inertia and force, in 

 their modern generalised aspect which formulates them under the 

 energy principle. The main problem of transcendental physics is to- 

 assign the nature of the ultimate medium or scheme of relations 

 which combines physical phenomena into a unity, in whose relations 

 these dynamical notions have their scope : and it is only the prejudice 

 of education that would keep, in this wider field, too close to the 

 ideal of mechanical transmission in a homogeneous elastic solid. 



In so far as we can collect the various dynamical principles into 

 a simple formula, we shall attain the security that all the trains of 

 results that come from that formula are consistent among themselves, 

 and form parts of a single interlaced scheme. Such a formula was 

 dimly foreshadowed by Maupertuis as the Principle of Least Action, 

 and after various elucidations by Euler was finally established in its 

 generality by Lagrange for ordinary material systems. The ultimate- 

 unification of physical theory, which transcends and includes ideas 

 of contact action and other partial explanations, would thus lie in 

 the formulation of the energy function of the sether, including- 

 matter, in a manner suitable for the application of the action 

 analysis to the correlation of the observed phenomena. To assume 

 that this will ever be accomplished absolutely and completely is 

 nearly the same as to assume infinite capacity in the human under- 

 standing : but exact knowledge of inanimate nature comes by a pro- 

 cess of analysing and classifying into types the main physical 

 agencies as they present themselves in bulk to our senses, and it is a 



