114 HEAT. 



electrified than it would be were there no electrification of its surface. 

 The resistance to rubbing absorbs kinetic energy, which, we suppose, 

 takes the form of electrical energy, and finally reappears as kinetic 

 energy in the particles moving to or from the electrified surface. The 

 increased resistance when electrification is taking place, i.e. when 

 kinetic is being turned into electrical energy, is well illustrated in 

 friction and induction electrical machines. It is a common experience 

 that they are more difficult to turn when they are in good order and are 

 generating electricity. The existence of electrical energy is further 

 supported by the occurrence of light and heat in the electrical discharge, 

 i.e. by the appearance of light-energy and heat-energy, which would 

 otherwise have to be thought of as arising de novo. 



In certain cases we have also the appearance of electrical phenomena 

 as the result of heating or straining bodies, and we must then suppose 

 that we have conversions of heat or strain energy into electrical 

 energy. 



Magnetic Energy. If a bar of steel is stroked with one pole of a 

 magnet in one direction, the motion of the magnet is resisted and 

 kinetic energy is lost ; it is then found that small pieces of iron are attracted 

 by the ends of the bar, and that attractions and repulsions are ex- 

 perienced between the ends of the steel bar and those of the magnet. 

 We have here another case of the development of kinetic energy not 

 accounted for by the immediate disappearance of potential, strain, or 

 heat energy. We have, then, to suppose another form of energy 

 Magnetic Energy differing from electrical energy in its mode of 

 production, and in the phenomena accompanying its existence, but 

 similar to it in that we have to suppose its existence in order to con- 

 nect the kinetic energy lost in magnetisation with the kinetic energy 

 appearing in the motion which we term magnetic action. 



The last two forms of energy, electric and magnetic, are closely 

 associated with each other, so that, in general, when we have trans- 

 formation of the one, we find that the other is present. In the electric 

 current, for example, we have every reason to suppose that there is 

 a transformation of electrical energy into heat taking place within the 

 wire ; and, accompanying this transformation, we have magnetic actions 

 round the wire, revealing the presence of magnetic energy there. Or, 

 in the dynamo-machine, we -have the transformation of kinetic energy 

 into electric and magnetic energies, both being associated to form the 

 energy of the current. Both electric and magnetic energies are forms 

 whose existence, like that of gravitational potential energy, we assume 

 as connecting links between energy disappearing when the electric and 

 magnetic conditions are produced, and energy appearing when those con- 

 ditions change. Some form of energy disappears during the production 

 of the conditions which we describe as electrification or magnetisation, 

 and we find that the same or other forms of energy may be made to re- 

 appear by the electric and magnetic actions. We have no special senses 

 which are affected by the electric or magnetic modifications of matter, 

 and they are therefore in some degree more hypothetical than Kinetic 

 energy, or Heat, or Light. 



Chemical Energy. Lastly, we have to recognise a form of energy 

 in Chemical Separation. Heat is necessary to decompose many sub- 



