MODERN SCIENCE. 181 



1777 1857. Thenard, in collaboration with Gay-Lussac, 

 obtained sodium and potassium by means of charcoal ; dis- 

 covered BORON, and also oxygenised water. 



17781829. Davy (Sir Humphrey) analysed LAUGHING 

 GAS (nitrous oxide) ; then by the DECOMPOSITION OF WATER 

 into its constituents (oxygen and hydrogen) by means 

 of the ELECTRIC PILE, he established a new method of 

 chemical analysis, called ELECTROLYSIS, or the decomposition 

 of substances by electricity. This was a fact of immense 

 importance because it showed electricity can overcome 

 chemical affinity (or attraction of elements to one another) 

 the power, in other words, which holds several elements 

 together in one compound substance. Faraday developed 

 electrolysis far beyond the point at which Davy left it. After 

 various analyses of compound substances, by means of the 

 powerful electric battery which he constructed for that 

 purpose, Davy established THE LAW : " Chemical affinity is 

 nothing but the energy of opposite electric powers" which led 

 Berzelius to his classification. By the means of the pile 

 Davy separated potassium, sodium, barium, strontium, 

 calcium, and magnesium from fixed alkalis thought to be 

 simple elements until then a discovery again which opened a 

 new era in chemistry. Davy also studied the production of 

 heat (by friction), and was led to the conclusion that "heat 

 is a peculiar motion, probably a vibration of the corpuscles of 

 bodies t tending to separate themselves" a proposition which he 

 proved by experiments thus establishing the doctrine inti- 

 mated by Lavoisier and Rumford a short time before, and at 

 the same time solving the problem of the cause of latent heat, 

 which had puzzled Black. He also upset the theory 

 (Lavoisier's) that oxygen was a necessary element of all acid 

 substances by his famous discovery of chlorine. After 

 numerous observations on flame, he invented the SAFETY- 

 LAMP (1815), which has saved thousands of lives. As early as 

 1802, soon after Ritter's discovery of chemical rays*, Davy 

 saw the possibility of taking images by means of solar rays 

 acting upon chloride of silver, and with Wedgwood actually 

 took some, but he did not succeed in fixing them perma- 

 * See W. Herschel. 



