MODERN CHEMISTRY. 463 



vexata among philosophers. The solution of the question, 

 when obtained, will doubtless equally apply to and illustrate 

 both. The opposite opinions of Volta and Wollaston, as to 

 the priority of action in these powers, were not reconciled by 

 Davy's researches. But Faraday has given confirmation to 

 Wollaston's view, and a more just expression of the general 

 theory, by proving that no chemical action can ever occur 

 without development of electricity ; and, conversely, that the 

 electrical force is never put into activity without some evi- 

 dence of chemical change. Thus regarded, the whole subject 

 becomes subordinate to that great law of the Co-relation of 

 Forces of which we have so often had occasion to speak. 



Still more briefly must we notice the relations between 

 chemical action and light. Their illustration through pho- 

 tography in its various forms has now become familiar to all. 

 If seeking another and less familiar example to denote these 

 subtle relations, we might find it in the curious influence of 

 solutions of sugar on polarised light passing through them, 

 and the variations of this influence by simple changes of 

 temperature. The test thus obtained is delicate enough to 

 show the particular quality, as well as quantity, of sugar in 

 solution, by the amount of deflection or rotation it produces 

 in the polarised ray. An instance of this kind carries its 

 interpretation far beyond the simple limits of the experi- 

 ment. It is an index of relations which pervade all nature. 



This short history of Modern Chemistry we must now bring 

 to a close ; though, in so doing, we omit many other dis- 

 coveries which have given lustre to the period under review. 

 Even in this outline, however, enough has been stated to 

 justify our assertion of the marvellous progress of the science, 

 and our anticipation of future results hardly less remarkable 

 than those already obtained. We have been careful to indi- 

 cate, as the subjects came before us, the probable paths of 



