100 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1736. 



At other times he has observed, when no air was by the way taken into the 

 bell, but the same lowered down the common way, and hauled up again after 

 some time, that the very instant when the bell should part with the surface of 

 the water, the strength of two men more was required at the capstan at that 

 time, than before and after the bell hung freely in the air; from whence he 

 thinks it plainly appears, that the air which passes through the lungs of an ani- 

 mal loses its elasticity, and that the lungs of a man make a kind of a vacuum 

 in the bell; for which re.nson the diver feels at the instant when the bell parts 

 with the water, a very smart pressure in his ears. 



Though experience thus has taught that no invention is more safe and useful 

 than the campana urinatoria, with the ingenious improvements of Dr. Halley; 

 yet M. Triewald has found, that this invention is not to be used without con- 

 siderable charge ; requiring a large vessel, and number of hands, to the work- 

 ing and managing of such a large diving bell, and the air barrels with their 

 respective weights for sinking; which charges however, according to the depth 

 of water, and the value of what is to be brought up from the bottom of the sea, 

 may not be regarded; but since it more frequently happens in these parts, that 

 cargoes of a far less value than the loadings of Spanish galleons, &c. are to be 

 dived for; then next to the goodness of the invention, he has found it neces- 

 sary to think how the expences might be lessened, and the diving bell still an- 

 swer all the purposes of Dr. Halley's; which improvement is as follows: 



The diving bell, ab, fig. 8, pi. 2, is made of copper, and reduced to a very 

 little compass, in respect to Dr. Halley's, by which means it is easily managed 

 by two hands: yet Mr. T. thinks that a diver may not only live in the same as 

 long, and with as much ease, at a very considerable depth of water, as in a bell 

 of twice its capacity, for this reason, though a man in a large bell has undoubt- 

 edly more air than in a less, and consequently should be able to subsist much 

 longer on a large quantity of air than on a small parcel: yet as his head is kept 

 chiefly in the upper part of the bell, occupied by the hot air, he receives very 

 little or no benefit from the air under his chin or breast, though never so fit for 

 respiration; which air in the lower parts of the bell will yet remain cool a long 

 time after he has been in the bell, and with difficulty drawn his breath; which 

 cannot be denied, and is very obvious to any who have been in a German 

 bagnio, and such as are made use of in this country, where in a single room all 

 the degrees of heat are to be felt, by means of a contrivance like stairs to the 

 very top of the ceiling; a man on the uppermost step feels an excessive heat, 

 so that one not much used to it cannot endure the same, nor draw his breath, 

 but will faint away; whereas on the first, second, and third steps from the 

 floor, the heat is very moderate; nay, sometimes the air near the floor pretty 

 cool, when at the same time near the ceiling the heat is intolerable. 



