COSMOS, VOL. II - World eBook Library

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 knowledge
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 nitroaereus
pabulum nitrosuni), which, contained in the air, and
identical with those which are fixed in salt-petre. were supposed
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
"
It was maintained that the
1669, and by Willis in 1671.
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 glow r
ing heat, when fusing salt-
petre (emitting oxygen), is strewed upon coals, and the formation
of saltpetre on clay walls in contact with the atmosphere
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 llobert 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 delusion
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
B. 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.)