CHAP. _7th. The elastic force of the Air depends on its nitro-aereal particles. In what way exhausted air is reimpregnated with them. Of the elements of Heat and Cold._ This chapter contains experiments to shew that the elasticity of the air is owing to the nitro-aereal particles contained in it: which may be destroyed by the burning of a candle or other combustible substances, and also by the breathing of animals. When the atmospheric air contained in a glass jar inverted over water, will no longer support flame or animal life, the water rises in the jar, owing to the diminished elasticity of the air, not being able to counteract the pressure of the surrounding atmosphere on the water p. 100. He finds p. 101 that the diminution by burning a taper in a given quantity of the air, is about one thirtieth of the whole, and by the breathing of mice and other animals about one fourteenth. Thence he concludes p. 106 that by means of respiration the elastic part of the air enters into the blood, and that the sole use of the lungs is not as some suppose, to break down the blood in its passage into very minute particles. That combustion and respiration have similar effects on atmospherical air, he concludes, p. 108, from the fact, that a candle and a small animal inclosed together in a glass jar over water, the one will not burn, nor the other remain alive above half the time that they would if alone. Mayow however, did not consider his nitro-igneous and elastic particles to be either pure air, or even a component part of the common air, as air, notwithstanding the ambiguity of the passages in p. 114 and 118; but as particles of a different nature, attached to and fixed in the atmospheric particles; and detached (_excussas_) by the means above mentioned, p. 118 and 121. His explanation of elasticity generally in this chap. and of the difficulty arising from the obvious resistance to the Atmosphere, and the expansibility of the air in which a taper has been extinguished, or an animal died, seem too obscure and unintelligible to merit transcribing. It is evident however upon the whole from p. 123 compared with p. 100 and 135 that he conceived the diminution of such air to arise from diminished elasticity, but he supposes it to be denser than common air 123. In a subsequent part of this chapter p. 128 et seq. he states his theory of the manner in which deteriorated air recovers its loss, viz. that the nitro-aereal particles being lighter than the atmospherical, float abundantly in the higher regions; and that the part of the atmosphere deprived of them below, being forced upward by the pressure of the atmosphere above, obtains a renewal of these particles by mixture with the strata where they abound.