174 Suggestions for the better Ventilation of 



vvald, an account of which was read before the Royal Society 

 of Sweden, 3d April 1742,* and a description of it published 

 by order of his Swedish Majesty, called a deduction of the 

 usefulness of his engine on board of ships only, and a trans- 

 lation of the work, was communicated by Cromwell Mortimer, 

 M.D., Sec. R.S. to Dr Hales. M. Triewald's ventilator drew 

 the foul air from under the decks of ships ; the least it exhausted 

 was 36,172 cubic feet of air per hour. In men-of-war and hos- 

 pital ships this machine was placed on the upper deck, directly 

 over the great, or any other hatch, and the pipe going down be- 

 tween decks drew out the unwholesome air, which was in- 

 stantly supplied by fresh. In 1742, all the men-of-war of the 

 Swedish navy were fitted with them, and in that year the 

 king of France ordered all his navy to be provided with these 

 ventilators. 



Dr Hales, in his Treatise, also mentions the ventilator of 

 Nathaniel Henshaw, M D., F.R.S., who printed an account of 

 it in a treatise called Aero Chalinos, or Register of the Air, 

 1677. Dr Hales gives the following account of it : — In order 

 to have the benefit of change of air without going out of the 

 house, he would have a room, which he calls an air-chamber, 

 to be built 12 feet square, and air-tight every where, with a 

 very large pair of organ bellows to be placed in the room, to 

 or from which air is to be conveyed through the wall by a 

 copper pipe, with valves to open inwards or outwards as occa- 

 sion shall require. With these bellows the air in the room is 

 either to be condensed, made heavier by forcing air in, or 

 lighter by conveying air out of the room. Should a person de- 

 sire to be in air so heavy as to raise mercury three inches, 

 then the air must be forcibly drove into the room by the bel- 

 lows ; and vice versa, it must be drawn out when it is required 

 to have the air so much lighter than the outward air. The 

 pressure to affect the air in the room would be immense ; 

 whether to condense or rarify it so much, it would be 38,304 lb. 

 troy in the opposite direction. He proposes by this means to 

 cure fevers, &c., the patient remaining in this chamber, as 

 also to prevent sea-sickness, by confining the person in such a 



♦ These Transactions are in the Library of the Royal Society of London. 



