INTRODUCTION. 



less fruitful in its influence on the sciences and arts. By its 

 principle, it has formed a new branch of science, photo-chemistry : 

 as to the services it unceasingly renders to the arts and to the 

 natural sciences, it is scarcely necessary to enumerate them. It 

 is true that for a moment this means of reproduction of natural 

 objects was injured by overrating the part to be taken by photo- 

 graphy, and by supposing it would be able to supplant the artist : 

 as if a mechanical process were capable of translating the sentiment 

 of the painter, that is to say, the poet in presence of nature, senti- 

 ment being the true source of inspiration, without which there can 

 be no masterpiece. The part filled by photography is both more 

 modest and more useful : it popularizes the chefs-d'oeuvre of painting, 

 statuary, architecture, and engraving ; it reproduces the smallest 

 details of natural views, of the objects studied by the geographer, 

 ethnologist, and naturalist ; and enables the poorest to preserve 

 the likenesses of those most dear to them, and in this sense it 

 has and always will have a moralizing influence. 



So much for the results. But if it is looked at from a scientific 

 point of view, is not this automatic reproduction of natural objects 

 marvellous this painting with no other agent but that of light ? 

 Moreover, each step taken in this art reveals surprise after surprise : 

 after photography comes heliography, which, if a few practical diffi- 

 culties can be conquered, will soon enable photogenic images to 

 be multiplied, just as typography multiplies books and ordinary 



V. 



I mentioned at the beginning of this introduction the most con- 

 siderable application of the phenomena and laws of heat, that which 

 is based on the transformation of heat into mechanical power. No 

 physical application can rival the steam-engine in the immensity 

 of its results. Socially speaking, it is by producing power that the 

 worth of man, whether we deal with the individual or the nation, is 

 estimated. 



Now, steam has increased the sum of the forces of which man 

 can dispose for the satisfaction of his wants : in an enormous 

 proportion it is just as if it had increased his capacity for work 



