120 PROGRESS OF SCIENCE IN THE CENTURY. 



rausch, 1880), or how the velocity of the migration 

 of the ions was calculated, or how equations have 

 been worked out and confirmed (Willard Gibbs, 

 Helmholtz, Jahn), showing the relation between the 

 chemical energy, the electrical energy, and the altera- 

 tion of the electromotive force (i.e., potential, ten- 

 sion or intensity) with the temperature, such that 

 any one of the three can be calculated if the other 

 two terms are known. But we have said enough 

 to suggest the fruitfulness of the co-operation of 

 chemistry and physics in the department of electro- 

 chemistry, and to suggest how well it will repay the 

 reader to avail himself of the pleasure which is af- 

 forded by modern chemistry, as expounded by mas- 

 ters like Ostwald. 



THE CIRCULATION OF MATTER. 



Transformations in Plants. We have already al- 

 luded to the chemist's power of transforming matter. 

 Out of coal-tar he brings the colours of the rainbow 

 and he makes the rubbish of twenty years ago a source 

 of riches to-day. 



But any common green plant is the seat of trans- 

 formations of matter not less marvellous. The ele- 

 ments of soil, water, and air are by the touch of life 

 lifted into complexity, united into organic com- 

 pounds, forming part of the capital of a living crea- 

 ture. 



We are also aware of what Mr. Grove long since 

 called the correlation of the physical forces, what 

 others speak of as the transformations of energy. We 

 know how the energy of the mill-race may drive a 

 dynamo, and we see the energy again in our electric 



