At the same time, air from the red precipitate was diminished in the same proportion as that from _mercurius calcinatus_, five measures of nitrous air being received by two measures of this without any increase of dimensions. Now as common air takes about one-half of its bulk of nitrous air, before it begins to receive any addition to its dimensions from more nitrous air, and this air took more than four half-measures before it ceased to be diminished by more nitrous air, and even five half-measures made no addition to its original dimensions, I conclude that it was between four and five times as good as common air. It will be seen that I have since procured air better than this, even between five and six times as good as the best common air that I have ever met with. FOOTNOTES: [Footnote 15: From _Experiments and Observations on Different Kinds of Air_, Vol. II, (1775).] XIV HENRY CAVENDISH 1731-1810 _Henry Cavendish, the discoverer of hydrogen, was born of English parents in Nice, October 10, 1731. He studied at Cambridge University, England, and in 1760 joined the Royal Society, devoting his great fortune to the advancement of science. He discovered hydrogen in 1766, and later, using Priestley’s discovery of oxygen, found that the two gases combined under certain physical conditions to produce water. Besides his studies in chemistry, he made some interesting discoveries in physics. In 1783 he proposed the theory that heat was a motion rather than a substance; and in 1798 he computed the density of the earth to be about five and a half times that of water. He died at Clapham, February 24, 1810._ THE COMBINATION OF HYDROGEN AND OXYGEN INTO WATER[16]