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Rh breathed air must be got rid of and sent outside into the ocean of the atmosphere.

It can not in fairness be alleged that those in authority were slow to avail themselves of the benefits of Hales^s ventilators; but their adoption in the prisons^ where the ventilation was excessively bad^ was no doubt hastened by the deaths of the Lord Mayor of London, two Judges and an Alderman, all of whom became infected with gaol fever caught at the. Old Bailey Sessions. "The Royal Society" wrote the late Sir William Huggins, "was called upon for advice and assistance. A committee was appointed to investigate the wretched state of ventilation in gaols. A ventilator invented by one of the committee was erected in Newgate, reducing at once the number of deaths from eight a week to about two a month. Of the eleven workman employed to put up the ventilator, seven caught the fever and died." There is not the slightest doubt that in those days to be sent to prison was the same thing as undergoing the death sentence of poisoning by foul air. Though Huggins does not mention Hales, it is certain he is the person alluded to as on the committee who introduced his ventilators into the prison. The version given by Peter Collinson in his sketch of the life of Hales (Annual Register for 1764) differs a little in one or two particulars: this writer states that in 1749 Hales's ventilators were installed in the Savoy prison by order of Mr. Henry Pox, later the first Lord Holland. Between the years 1749 and 1752. four prisoners died there of gaol fever as compared with between fifty and a hundred per annum previously. In the year 1760, out of two hundred and forty prisoners, only four died; and of these two died of smallpox and one of alcoholism, so that the salutary effects of Hales's installation were immediate and striking. In 1752 his ventilators actuated by a wind- mill and having ducts leading from twenty-four cells or wards were introduced into Newgate prison: as a result of this, Collinson says, the ratio of deaths after to those before the ventilation was as seven to sixteen, that is they had been reduced to less than 50 per cent. In 1763 Hales wrote an article in the Oentleman's Magazine on the ap- plicability of his ventilators to army hospitals and to private houses. He also reported on their means in a smallpox hospital. Before his death his ventilators had been installed in the prisons at Winchester and Durham. In modern terminology. Hales ventilated by abstraction of foul rather than by propulsion of fresh air.

Hales's invention was greatly appreciated on board ship. Ships at this time were floating strongholds of death; between scurvy and ship fever due to poisoning by bad air, only the most robust men survived for any length of time. In 1755, Hales wrote a short but most interesting paper to the Royal Society, entitled "An account of the great benefits of ventilators in many instances in preserving the health and lives of people in slave and other transport ships." In this, Hales