210 PROl-EKTIES OF AIR 



could judge, not having a watch upon me at 

 the time. I certainly did not believe it possi- 

 ble for men to swim perpendicularly down- 

 wards to the depth of 11 fathoms, and execute 

 a laborious task there, until I witnessed this 

 undertaking. 



" I have heard it said, that the pearl divers, 

 in the Gulf of Persia, descend into depths of 

 30 or 35 fathoms, to procure the oysters, by 

 means of a heavy stone fixed to their feet by a 

 strap ; as soon as they reach the bottom, they 

 shake the stone clear of their feet, and gather 

 the oysters into a bag they have for that pur- 

 pose; and when they want to ascend, they 

 pull a cord which is connected with the boat, 

 or vessel, and they are immediately drawn up, 

 very speedily, by the persons stationed for that 

 purpose," 



If we, therefore, admit the estimate which is 

 generally made, that a cubic foot of water 

 weighs 64 Ib. and that a man at the bottom of 

 the sea, at the depth of 30 fathoms, exposes two 

 square feet of the surface of his body to the per- 

 pendicular pressure of the column of water ; it 

 will be found, that by multiplying 180, the num- 

 ber of feet, by 128, the number of pounds ; that 

 he must have sustained a pressure equal to 

 21-600 Ib. I shall not attempt to show the folly 

 of such a conclusion by any further detail. If 





