238 PROGRESS OF SCIENCE. 



however, is stoutly contested as we just hinted, and there- 

 fore by no means finally determined. Faraday made 

 numerous observations in optics ; invented several kinds of 

 optical glasses; discovered the phenomena and the three 

 LAWS OF ELECTROLYSIS that is, the process of decomposition 

 of substances into their elements by the voltaic battery, 

 which Davy had found "Electrolysis cannot take place unless 

 the substance be a good conductor," being the most important 

 of the three. He also showed that the current does not depend 

 upon the effect that two metals may have upon each other, 

 which was Volta's theory, but is produced by the chemical 

 action taking place between the water and the zinc ; and in 

 order to show the strength of the decomposition taking 

 place, and therefore ascertain the intensity of the current, he 

 invented the VOLTAMETER. The knowledge of this pheno- 

 menon led him to demonstrate that the chemical change gives 

 rise to electricity, just as electricity also produces chemical 

 change another transformation of force. Faraday also 

 formulated the THEORY OF INDUCTION (influence) the 

 mode of action of electricity on which a vast number of 

 electrostatic phenomena closely depend, and chiefly the action 

 of electrified bodies on bodies in their natural state. Of 

 all electric phenomena the most important is induction, 

 because it is tc on account of induction that we can observe 

 electricity at all ; every manifestation charge, discharge, 

 attraction, repulsion is preceded by and dependent upon in- 

 duction. If an uncharged conductor be brought near to an 

 electrified body, and thus placed under its influence, the un- 

 charged body assumes an excited state, one side of it being 

 electrified similarly, the other oppositely, to the charged body. 

 The propagation of electric force across a non-conducting 

 medium is called induction" Faraday, finally, determined 

 the inductive power of various substances. Our limits do not 

 allow us to dwell upon, or even allude to, the very numerous 

 investigations carried on, and the invaluable services rendered 

 to science by this great inquirer. 



iyqi j8 . Pouillet invented the PYRHELIOMETER to 

 ascertain the amount of heat emitted by the sun the heat 

 would boil 700,000 millions of cubic miles of ice-cold water 



