INTERACTION OF NATURAL FORCES. 



ANEW conquest of very general interest has been recently 

 made by natural philosophy. In the following pages, I 

 will endeavour to give a notion of the nature of this conquest. 

 It has reference to a new and universal natural law, which 

 rules the action of natural forces in their mutual relations 

 towards each other, and is as influential on our theoretic 

 views of natural processes as it is important in their technical 

 applications. 



Among the practical arts which owe their progress to the 

 development of the natural sciences, from the conclusion of 

 the middle ages downwards, practical mechanics, aided by 

 the mathematical science which bears the same name, was 

 one of the most prominent. The character of the art was, at 

 the time referred to, naturally very different from its present 

 one. Surprised and stimulated by its own success, it thought 

 no problem beyond its power, and immediately attacked some 

 of the most difficult and complicated. Thus it was attempted 

 to build automaton figures which should perform the functions 

 of men and animals. The wonder of the last century was 

 Vaucanson's duck, which fed and digested its food ; the flute- 

 player of the same artist, which moved all its fingers cor- 



