30 Prof. Oliver Lodge on 



undynamical blinkers appropriate to the consideration of 

 particles in the lump. 



Appendix 1. — The Objectivity of Energy and 

 the Question of Gravitation. 



Mr. Heaviside* freely contemplates the flux of energy, but 

 declines to admit its identity, or as he calls it objectivity. 

 And he further doubts my proposition about transformation 

 accompanying transference, because, he says, " convection of 

 energy/" i. e. simple locomotion of stored energy, "is a true 

 flux/' So it is, but it is not what I meant by transfer. 

 Locomotion is so absolutely essential to translational kinetic 

 energy that I hardly think it can be desirable ever to speak 

 of mere locomotion as transfer, even although the moving 

 thing be a bent bow or stretched spring. It is, however, a 

 question of convenience, and undeniably convection must 

 enter into a flux equation, for a bullet entering a partitioned- 

 ofF region of space brings into it energy which was not there 

 before, and, when it leaves, conveys it out again. 



My proposition amounts to just this, that whatever energy 

 appears in a bounded region must necessarily have passed 

 through the boundary. This, if true, seems to me to confer 

 upon energy the same kind of identity or continuous existence 

 (or if you please objectivity) as matter possesses. 



The ordinary law of conservation does not assert or con- 

 template continuous existence : it has no objection to seeing 

 energy disappear from existence in one place provided an equal 

 quantity reappears somewhere else — say inside a bounded 

 region. Either it does not attend to or believe in the fact of 

 transfer, or else it is satisfied with a kind of fourth-dimen- 

 sional out-of-space path. 



As to " objectivity " or " reality/' there are always meta- 

 physical difficulties about predicating that ; and Mr. Heavi- 

 side's objection that since motion is relative, energy can 

 hardly be absolute, must be allowed due weight. This is a 

 point on which Professor Newcomb has written in Phil. Mag. 

 February 1889 ; arguing that it actually limits the generality 

 of the law of conservation. I hope some day to discuss this 

 at more length ; meanwhile my belief is that it will be 

 ascertained that motion with respect to the ether is the 

 energetic thing and that other absolute motion is meaningless. 

 The fact (if fact it be) that energy has a continuous 

 existence, or that if it appears in a closed region it must 



* Phil. Trans. 1892, p. 427, " On the Forces, Stresses, and Fluxes of 

 Energy in the Electromagnetic Field," by Oliver Heaviside, F.R.S. 



