296 PRESSURE IN THE Allt, 



of the bladder was the effect, it must unavoid- 

 ably follow, that this effect was accomplished 

 from the weight of the air between the cylinder 

 and the receiver, and which before was ascer- 

 tained to amount to 10 grains only. On plac- 

 ing, howeVer, a weight over the bladder, not of 

 10 grains, but of 18 pounds, it was found capa- 

 ble of supporting it, without suffering any lesion 

 whatever. 



As the weight placed upon the bladder co- 

 vering a full receiver, may not be considered 

 to be under the same circumstances as it is, 

 when the air is exhausted out of it; and with a 

 view of ascertaining what degree of weight is 

 absolutely necessary to burst the bladder, ab- 

 stractedly from the air ; I stretched a bladder 

 upon an open frame, and placed upon it a 

 weight of 18 pounds, and over it a receiver; 

 on exhausting the air out of the receiver, the 

 bladder was enabled to support the weight, 

 without being ruptured, equally well as if it 

 had been exposed to the open air. It is, there- 

 fore, legitimate to conclude, that although the 

 effect produced, the bursting of a bladder over 

 an exhausted receiver, is caused by the pres- 

 sure of the air, yet, that it is not caused by the 

 pressure of weight, but is to be referred to the 

 pressure of expansibility alone, which air has 

 been proved to possess ; which expansibility is 



