Sailing and Steam- Vessels. 175 



cabin. Dr Hales says, some have said his ventilator and this 

 are the same ; but he declares their difference is wide in prin- 

 ciple ; besides, the make of his is very different from organ bel- 

 lows. He then gives an account of his ventilator, which has 

 the merit of being easily and cheaply constructed ; and as it 

 was much valued at the time, and long afterwards, I shall give 

 a short description of it. It consisted of two oblong air-tight 

 boxes, placed parallel to each other, having wooden boards, 

 or midriffs, closely fitting the interior section of these boxes, 

 hinged at one end, and drawn up or pushed down at the oppo- 

 site end by means of upright iron rods attached to a lever, 

 moving on a standard between the boxes. By the elevation 

 or depression of the midriff, effected by the alternate raising 

 and depressing the ends of the lever, the air was drawn in or 

 forced out of the boxes, by a series of valves, some opening in- 

 wards and some outwards, at the opposite end from where 

 the iron rods were ; there was a casing placed over four of the 

 valves which emitted the foul air, communicating with an 

 air-trunk, or pipe, which led off the air in one body. But 

 without drawings, it is not easy to convey a correct idea of the 

 machine. It could be used either to throw in fresh, or to draw 

 off foul air. Dr Hales describes the application of his ventila- 

 tor to H. M. Ship Captain. The ventilator was about 10 feet 

 long, 5 feet wide, and 2 feet deep. It was placed flush, or even, 

 with the floor of the orlop deck, and the trunk or vitiated air- 

 pipe went through the gun and upper decks, near the side of 

 the ship to the top of the gunnel. Two men, standing on the 

 orlop deck, worked the lever, which was 12 feet long ; and, from 

 the number of men in large ships, the labour was small. The 

 lever and standard were made to unship, so that little obstruction 

 arose from this machine. The air to supply that which was 

 pumped off passed down the hold by the open hatches, or other 

 means provided, and the current was so gentle as not to be per- 

 ceptible. From the number of open passages, its motion was 105 

 times slower than when passed off at the orifice of the ventilator. 

 When the hold is to be ventilated, the doors into the gun- 

 ner's store-room are opened, and all the gratings on the gun- 

 deck covered with tarpaulins, leaving all the doors open of 

 those cabins or rooms which want ventilation. The vcntila- 



