176 Suggestions for the better Ventilation of 



tors were made of different sizes, according to the class of the 

 ship. A large sized one for a first or second-rate is already 

 given, and for a 50-gun ship Dr H. proposed it should be 4 feet 

 3 inches wide, 9 feet long, 1 foot 6 inches deep, trunk 10 square 

 inches ; for a 20-gun ship, 8 feet long, 4 feet wide, 1 foot 

 6 inches deep, pipe 9 square inches. Smaller ventilators were 

 also made of only one box, portable for such a purpose as air- 

 ing the bread-room of ships, sweetening water, &c., having an 

 iron rod and cross handle to raise the midriff. One person 

 could easily work it for a length of time. Dr Hales strongly 

 recommended his ventilator for blowing air through water in 

 showers for sweetening it ; also for milk in a similar way, and 

 for airing corn, and for a variety of other purposes. 



In 1751, in reference to Dr Hales' ventilator, there are some 

 experiments recorded in a letter from Captain H. Ellis, ship 

 Earl of Halifax, Phil. Trans., London, shewing its utility, — 

 that the ventilator was far from being inconvenient on ship- 

 board, and that out of a ship's crew of 130 men, there was not 

 one sick on board. So much was Dr Hales' ventilator afterwards 

 valued for ship ventilation, that an order in 1756, for venti- 

 lating the fleet, was issued by the Lords of the Admiralty. — 

 (Eees' Enc, and 3d edit. Enc. Brit.) The ventilators were 

 fixed in the gunner's fore store-room, and generally a-head 

 of the sail-room, varying according to the class of the ship. 

 The power of the large ventilator was very great. At 60 

 strokes per minute, the speed at which the greatest quantity 

 of air was found to be emitted, 75 tons of air were discharged, or 

 4500 tons per hour, or 108,000 in 24 hours ; the velocity of the 

 air upwards was at the rate of 3000 feet per minute, or at an 

 average rate of 26 miles per hour. In the year 1752, Dr Hales' 

 ventilators, it is recorded, were very successfully applied to 

 ventilate Newgate prison, and placed in the upper part of the 

 building, when, being worked by a wind-mill, they drew out 

 the foul air from several wards.* — Gent. Mag. vol. xxii. 



Notwithstanding the acknowledged success of these venti- 

 lators in ships, mines, and prisons, still on shipboard there 

 must have been objections raised against them, as Dr Hales, 



* Hales' Treatise, vol. ii., London, 1758. 



