VOL. XXIX.] PHILOSOPHICAL TRANSACTIONS. 26l 



steady. This machine I suspended from the mast of a ship, by a sprit, which 

 was sufficiently secured by stays to the mast-head, and was directed by braces to 

 carry it over-board clear of the ship side, and to bring it again within-board as 

 occasion required. 



To supply air to this bell when under water, I caused a couple of barrels, of 

 about 36 gallons each, to be cased with lead, so as to sink empty ; each having 

 a bung-hole in its lowest part to let in the water, as the air in them condensed 

 on their descent ; and to let it out again, when they were drawn up full from 

 below. And to a hole in the upper part of these barrels I fixed a leather trunk 

 or hose, well liquored with bees-wax and oil, and long enough to fall below the 

 bung-hole, being kept down by an appended weight ; so that the air in the 

 upper part of the barrels could not escape, unless the lower ends of these hose 

 were first lifted up. 



The air-barrels being thus prepared, I fitted them with tackle proper to make 

 them rise and fall alternately, after the manner of two buckets in a well ; which 

 was done with so much ease, that two men, with less than half their strength, 

 could perform all the labour required : and in their descent they were directed 

 by lines fastened to the under edge of the bell, which passed through rings 

 placed on both sides of the leather hose in each barrel ; so that sliding down by 

 those lines, they came readily to the hand of a man, who stood on the stage 

 on purpose to receive them, and to take up the ends of the hose into the bell. 

 Through these hose, as soon as their ends came above the surface of the water 

 in the barrels, all the air that was included in the upper parts of them was blown 

 with great force into the bell, while the water entered at the bung-hoies below, 

 and filled them: and as soon as the air of the one barrel had been thus received, 

 on a signal given, that was drawn up, and at the same time the other descended ; 

 and by an alternate succession furnished air so quick, and in so great plenty, 

 that I myself have been one of five who have been together at the bottom, in 

 9 or 10 fathoms water, for above an hour and half at a time, without any sort 

 of ill consequence : and I might have continued there as long as I pleased, for 

 any thing that appeared to the contrary. Besiides, the whole cavity of the bell 

 was kept entirely free from water, so that I sat on a bench, which was diame- 

 trically placed near the bottom, wholly dressed with all my clothes on. I only 

 observed, that it was necessary to be let down gradually at first, as about 12 

 feet at a time ; and then to stop and drive out the water that entered, by re- 

 ceiving 3 or 4 barrels of fresh air, before I descended further. But being 

 arrived at the depth designed, I then let out as much of the hot air, that had 

 been breathed, as each barrel would replenish with cool, by means of the cock 



