iSyi.] Relations between Chemical Change, &c* 77 



perfect vitality, when carbonic acid is decomposed and 

 oxygen set free, and ending with death and decomposition 

 when the opposite change occurs. 



I More or less green-brown. 

 Low vitality and (ErythrophyU (crimson-red) } M ore or less red-scarlet, 

 change .. .. [ Xanthophyll (bnght yellow) ) j Mor£ Qr ^ bright orange _ 



Death and decom- ( Phaiophvll (brown-orange) [ | T^^more dull brown, 

 position . . . . ( Humus (brown-black) J 



According to these principles, we must look upon the pro- 

 duction of the fine tints of autumn as evidence of the 

 diminished vital powers of the plants. I presume that this 

 can admit of no doubt, and it agrees with the fact of 

 unhealthy branches of a tree turning yellow whilst the rest 

 remain green. The subsequent development of more sombre 

 tints is evidence of more complete death. Perhaps some of 

 my readers may think that such an explanation robs the 

 fading leaves of autumn of much of their poetry, but, at 

 the same time, I trust that the facts I have described may 

 tend to explain many of the beautiful and varied tints 

 which delight us so much in autumn, and that a knowledge 

 of such general laws will compensate for any loss of poetic 

 sentiment. 



VII. ON THE RELATIONS BETWEEN CHEMICAL 

 CHANGE, HEAT, AND FORCE, 



WITH A SPECIAL VIEW TO THE ECONOMY OF ELECTRO- 

 DYNAMIC ENGINES. 



By the Rev. H. HiGHTON,M.A^late Principal of Cheltenham 

 College, and Fellow of Queen's College, Oxford. 



Chapter I. 



JU THINK I may say, first, that the theory at present 

 Al generally accepted, and which it would be considered 

 somewhat heretical to deny, is this ; that a certain 

 amount of chemical change corresponds, and is interchange- 

 able with a certain amount of heat and electric force ; and 

 that this heat again corresponds and is interchangeable with 

 a certain amount of work or mechanical energy. This is, no 

 doubt, a very pretty, plausible, and apparently philosophical 

 theory ; but, is it true ? or, how far is it true ? This is the 

 question I now propose to consider, with a special view to 



