i/2 PROGRESS OF SCIENCE. 



Once again we repeat that this kind of logic was typical 

 of former ages ; new doctrines and new principles of thought 

 were so distasteful to those who considered themselves as 

 "the directors" of opinion, that the most inane pieces 

 of sophistry were put forward as valid arguments in support 

 of extravagant opposition, as if mankind, senseless and 

 ignorant, could be crammed with anything. Brazen as- 

 surance seemed the only essential wanted to ensure authority. 



GROUP III. CHEMISTRY. 



1626 91. Boyle proved by experiments air to be neces- 

 sary for COMBUSTION ; that a candle cannot burn nor animals 

 live without air ; he pointed out that the globe contains other 

 substances than those recognised in his times earth, water, 

 air, and fire; discovered (1661) the LAW that bears his name, 

 and which is also called Mariotte's law, of the COMPRESSI- 

 BILITY OF GASES the law, that is, of elasticity of air, the 

 formula of which is, " The temperature remaining the same, the 

 volume of a given quantity of gas is inversely as the pressure 

 which it bears )} in other words, the volume of a gas 

 decreases in proportion as the weight upon it increases 

 if you double the pressure, you halve the volume. We shall 

 see the vast importance of this great discovery, one of the 

 most serviceable in our possession, our modern industry and 

 wealth being largely dependent upon it. Boyle also improved 

 Guericke's air-pump. 



1645 79. Mayow, the best chemist of the XVIIth, 

 pursuing Boyle's experiments on COMBUSTION and respira- 

 tion, discovered air to be composed of two gases one, which 

 he called FIRE-AIR (oxygen), and which is heavy, supports 

 a flame and life, and is consumed by combustion and 

 breathing ; another, which is lighter, and is useless for 

 breathing and burning the nitrogen of Lavoisier thus going 

 further than Harvey in showing air to be the chief agent 

 in respiration, and going half-way towards the discovery of 

 Priestley and Lavoisier in showing air to be a compound 

 gas. He discovered also that " air exists in salpetre and in 

 many acids." 



