INDUCTION AND DEDUCTION, 263 



and the deductive labor of Weber is here quite apparent. Faraday 

 sought, if we may use the expression, the tiling; Weber the principle or 

 thelato. I have heard mathematical physicists regret thatFaradny's trea- 

 tises on such subjects were, iu point of style, nearly unintelligible and 

 scarcely readable, and that their tenor much resembled an extract from 

 a day-book; but the fault was in themselves. Upon physicists who 

 have advanced by the way of chemistry to physics, Faraday's treatises 

 make much the impression of wonderfully fine music. 



The discovery of the electrical machine, the electrophore, the Leyden 

 jar, the voltaic pile, as well as of the three laws of Kepler, has been 

 achieved through the combinations of the imaginative power; and so it 

 is also with the procedures for the extraction of metals, which, as that 

 of iron from iron-stone, of silver from the lead ores, and of copper from 

 the copper ores, are among the most complicated of processes. The con- 

 version of iron into steel, of copper into brass, the transformation of 

 hide into leather, of fat into soap, of common salt into soda, and a thou- 

 sand similar important inventions, have been made by men who had no 

 idea, or a wholly false one, of the proper nature of the things or pro- 

 cesses to which they directed their powers of ideal combination. 



The understanding has not the least to do with the combinations of 

 ideas which have carried the manufacturer of glove leather to the tow- 

 ers of the city in order to collect for his purposes the white excrement 

 of daws and rooks, or which have led the dyer to employ that of the 

 cow for fixing on stuffs his mordants and colors, or which, on the lofty 

 plains of America, so poor in combustible material, prompted the miner 

 to the singular expedient of obtaining silver in the wet way. All this 

 will undoubtedly appear remarkable enough when it is remembered that 

 until a few years past, the proper nature of glass, soap, and leather was 

 unknown, and that researches are still daily made to determine precisely 

 the reactions which take place in the melting-oven during the soda 

 process. 



As a last example of the inductive procedure in technical processes 

 I will select the lately discovered art of producing light-images — pro- 

 cesses, however, which have not yet found an exj)lanation. The facts 

 which lie at the foundation of j)hotography are two : The one that the 

 salts of silver (the chlorine, bromine, iodine of silver) are rendered black 

 by the light ; the other that the unblackened combinations of silver are 

 soluble in sub-sulphurated natron, so that the blackened and the un- 

 blackened may be separated from one another by means of this salt. 



These two facts formed the starting point of the experiments of Da- 

 guerre in Paris and of Talbot in London ; the first sought to produce 

 images on silvered copper-plates, the other on paper. When, in the 

 camera obscura, an image of a tower or of a house, for instance, is 

 thrown on paper overspread or saturated with chlorine or iodine of sil- 

 ver, there arises in Talbot's experiments, after some hours' exposure to 

 the operation of the light, a corresponding image j the more lustrous 



