of the various Forms of Energy, 283 



[The numbers in the compartments are merely for convenience 

 of reference.] 



It is quite possible that the form of energy indicated in compart- 

 ment No. 4. would be better placed in No. 8, those now in No. 8 

 being placed in No. 12 ; but I have placed them as they now stand 

 because they are closely connected with the vibration-forms in the 

 same rows. Moreover the true position of gravitation energy cannot 

 be properly denned till we know more about it. It may have to 

 come under the kinetic head — the motion of Le Sage's corpuscles. 



Probably the arrangement of the forms in the last row may be 

 improved, but I am not sufficiently acquainted with the Maxwellian 

 theory to do it. Neither do I know whether one is justified in 

 pointing out an analogy between the two forms of strain indicated 

 in No. 20 and simple and torsional shear, — or whether one may 

 imagine that the volume-elasticity and Young's modulus of the 

 " something" are infinite, but that its rigidity is finite though high. 

 An apparently consistent though rather hazy mental image of some 

 obscure phenomena may be built up on a basis like this ; but it is 

 too speculative to be mentioned further here. 



14. The power of doing work conferred upon a body by the 

 possession of energy does not depend upon the absolute quan- 

 tity of that energy only, but on its transferability. If it is 

 not transferable, the body possessing it has no power of doing 

 work. 



15. Energy which can be guided, and all, or nearly all, 

 transferred to any body at pleasure, is called a high or avail- 

 able form of energy, and is said to be capable of doing " useful" 

 work, this work being done every time it is transferred in 

 desired directions. 



Energy which is nearly incapable of being guided, and 

 which transfers itself in directions not required, is called a low 

 or unavailable form of energy ; and the work done at each of 

 its undesired transfers is called u useless " work*. 



16. The distinction between high and low forms of energy 

 is a relative one, and depends on our present power of dealing 

 with matter. 



Masses of matter comparable to our own bodies in size can 

 be handled and dealt with singly ; and so they can in general 

 be caused to do work upon, and therefore transfer their energy 

 at pleasure to, any of the numerous accessible bodies which 



* The distinction between useful and useless work is quite accidental, 

 and belongs more to economics than to physics. An engineer will often de- 

 grade the whole of a large quantity of energy in order to produce some 

 superficial result which lie happens to desire at the moment, c. g. when a 

 planing-machine smooths a surface ; or when a locomotive transfers pas- 

 sengers or goods between places on the same level. 



