DISCOVERY IS BOTH INDUCTIVE AND DEDUCTIVE. 187 



conditions a simpler force is resolved into a more complex 

 one, under other circumstances the latter is resolved into the 

 former. For instance, in thermo-electric action the single 

 self-repellent motion of heat is converted into the two 

 motions of positive and negative electricity, and at the 

 same time the two latter, by reuniting, reconstitute heat, 

 and these two reverse actions of heat and electricity are 

 equivalent. Whilst also on the one hand all the physical 

 and chemical powers produce heat, heat on the other hand 

 is the great source of physical and chemical power. As a 

 further proof that the development of the simple sciences 

 is dependent upon the progress of the more complex ones, 

 it may be remarked, that the knowledge we at present 

 possess respecting the molecular structures and motions in 

 substances, regarded as a basis for forming a mechanical 

 theory of physics and chemistry, has been chiefly obtained 

 by the aid of methods belonging to the more complex 

 sciences of light, heat, electricity, magnetism, and che- 

 mistry. 



Whilst also scientific discovery gives rise to complex 

 arts and manufactures, the latter react upon science to 

 assist discovery. ' Think of the immense improvements in 

 instruments for the measurement of electric charges and 

 electric currents, such as electrometers and galvanometers, 

 which have been effected, because called for, by the recent 

 extensions of submarine telegraphy. It is not too much 

 to say that the instruments now employed, and which were 

 primarily devised for practical telegraphic purposes, are 

 hundreds of times more sensitive, as well as more exact, 

 and therefore more useful for purely scientific purposes, 

 than the best of those which were in use thirty years ago. 

 Thus it is that a development of science, in a practical 

 direction, leads to the construction of instruments which 

 have, as it were, a reflex action on the development of the 



