128 ELEMENTARY GENERAL SCIENCE CHAP. 



action. The coal enters into a chemical combination with one 

 of the constituents of the atmosphere, and in doing so, heat is 

 evolved, as it is, indeed, in all cases of chemical combination. 



But as we shall soon have occasion to study many cases of 

 chemical action, we need not spend much space over the matter 

 here, though it must be pointed out that, just as in all 

 the other instances of energy we have studied, not only is 

 it true that chemical action is accompanied by changes of 

 energy, but also that it can result from these other forms. 

 Light can be made to bring about chemical action, as it does 

 in the case of the exposed photographic plate. Electric 

 separation or the energy of electrification also causes . chemical 

 action, as will be seen later. 



Transformation of Energy. We have learnt that one 

 kind of energy can cease to exist in that particular form, 

 and can assume another condition. We have seen that 

 the energy of moving bodies can give rise to sound and heat ; 

 that heat can be changed into the energy of moving bodies, 

 electric currents, and chemical action. Indeed, one form of 

 energy can assume almost any other form. The general 

 tendency of all forms of energy is gradually to get converted 

 into heat. When this change has become complete and all the 

 energy of the universe exists as heat at the same temperature, 

 there will be no further transformations possible. Consequently 

 no work of any kind will be possible, which means there will be 

 no life, 110 movement of bodies from place to place a still, dead 

 world, in fact. 



Conservation of Energy. We have seen that matter cannot 

 be destroyed ; we have now to learn that energy is inde- 

 structible. The total amount of energy in the universe remains 

 the same. One form may be changed into another, but we can 

 create no new energy. We may be unable to trace and account 

 for some of it in the numerous transformations which it under- 

 goes, but we are sure, from many considerations, that if our 

 methods of experiment were only refined enough, we should be 

 able to account for the whole amount. 



The great source of energy in the solar system is the sun. It 

 is from the sun that we are continuously receiving streams of 

 energy in the form of radiation, which are continually assuming 

 the various other forms of energy we have considered. Returning 

 once more to our steam engine, we have traced back the work it 





