730 COSMOS. 



Men had now discovered the path which was to lead them 

 to the chemistry of the present day, and through it to the know- 

 ledge of a great cosmical phenomenon, viz., the connection, 

 between the oxygen of the atmosphere and vegetable life. 

 The combination of ideas, however, which presented itself to 

 the minds of distinguished men, was strangely complicated in 

 its nature. Towards the close of the seventeenth century, a 

 belief arose in the existence of -nitrous particles, (spiritus nitro 

 aereus pabulum nitrosum'), which, contained in the air, and 

 identical with those which are fixed in salt-petre, were sup- 

 posed to possess the necessary requirements for combustion, 

 an opinion which obscurely expressed by Hooke in his Micro- 

 graphia (1671), is found more fully developed by Mayow in 

 1669, and by Willis in 1671. " It was maintained that the 

 extinction of flame in a closed space, is not owing to the 

 over-saturation of the air with vapours emanating from the 

 burning body, but is the consequence of the entire absorption 

 of the spiritus nitroaereus contained in the nitrogenous air." 

 The sudden increase of the glowing heat, when fusing salt- 

 petre (emitting oxygen), is strewed upon coals, and the for- 

 mation of saltpetre on clay walls in contact with the atmo-'- 

 sphere appear to have contributed jointly to the adoption of 

 this view . The nitrous particles of the air influence, according 

 to Mayow, the respiration of animals, the result of which is to 

 generate animal heat and to deprive the blood of its dark 

 colour ; and while they control all the processes of combustion 

 and the calcination of metals, they play nearly the same part 

 in the antiphlogistic chemistry as oxygen. The cautious and 

 doubting Robert Boyle was well aware that the presence of a 

 certain constituent of atmospheric air was necessary to com- 

 bustion, but he remained uncertain with regard to its nitrous 

 nature. 



Oxygen was to Hooke and Mayow an ideal object a delu- 

 sion of the intellect. The acute chemist and vegetable phy- 

 siologist, Hales, first saw oxygen evolved in the form of a gas, 

 when in 1727, he was engaged at Mennige in calcining a 

 large quantity of lead, under a very powerful heat. He 

 observed the escape of the gas, but he did not examine its 



g. 131-133. (Compare also in the same work, Th. i. s. 116-127, and 

 Th. iii. s. 119-138, as well as s. 175-195.) 



