442 THE SCIENTIFIC MONTHLY
health it is not too much to say that as a benefactor of mankiiid, he is conspicuous in the first half of the eighteenth century. It would be difficult to mention the name of any other person co-equal with his. We know very little indeed of his capabilities as a pastor of men's souls, but it is certain that he had great solicitude for their bodies; he intro- duced a water-supply into the village of Teddington, and it appears that he actually contrived to ventilate its parish church. His pamphlet against the abuse of alcohol is probably the first of its kind in English — "A friendly admonition to the drinkers of gin, brandy and other spirituous liquors.*' This, published in 1734, alone enables him to rank as a pioneer in the advocacy of measures of practical hygiene. Hales had grasped the very essence and kernel of the principle of venti- lation, that air must he changed, whether air for plants or for animals, air over com in granaries or over water stored for drinking purposes or air enclosed in hot-houses, or air in mines, or in the holds of ships, or in prisons, or around timber or gunpowder; air must be changed. He knew that fresh air was inimical to putrefaction, mouldiness of every kind ; he invented an apparatus for blowing air through drinking water stored in ships. On long voyages in the *'old wooden walls such water became putrid: Hales showed that it could be made sweet again if only enough air could be blown through it. We now know what was going on, namely the oxidation of organic matter; but Hales died in 1761, thirteen years before oxygen was discovered. It is inter- esting to note that Hales had the most definite conceptions as regards this necessity for oxygen in ventilation, without knowing what it was that sustained life, and without knowing, in anything like its fulness, the meaning and importance of Joseph Black's discovery that animals exhaled carbon dioxide from their lungs. Black's discovery was pub- lished in 1764, some seven years, indeed, before Hales died; but it is certain that Hales was not indebted to Black ; on the contrary, it is not as widely known as it might be that Black was profoundly indebted to Hales. Black wrote :
I was partlj led to these experiments by eome observations by Dr. Hales, in which he says that breathing through diaphragms of cloth dipped in alkaline solution made the air last longer for the purposes of life.
Before we further examine the value of the contributions made by Hales to the hygiene of ventilation, it will be well to trace the order of the discoveries of the gases of the atmosphere without which, of course, in the long run no scientific basis for the study of the problems of venti- lation could have been arrived at. Carbon dioxide was discovered under the name of gas sylvestre by the Belgian chemist J. B. van Helmont (1577 to 1644) about the year 1640. Having burnt a known weight of wood, he noticed that only about one sixtieth of the original weight remained in solid form. The other fifty-nine sixtieths he regarded as
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