C 348 ] 
perhaps as great a degree of vacuum is made in one 
cafe as in the other. 
2. It is probable, from thefe fa£Is, that animal 
bodies can bear much greater variations of the pref- 
fure of the atmofphere, than the natural ones, 
without any degree of inconvenience. Some who 
have afcended high mountains are faid to have been 
feized with a fpitting of blood : but as this never 
happens to animals, that are put into the exhaufted 
receiver of an air-pump, where the diminution of 
preflure is many times greater than on the fummit 
of the higheft mountains, it is probable it was an 
accidental difeafe, or was owing to fome violent exer- 
tions in afcending. And in the curious account Dr. 
Halley gives of his defcending in a diving-bell fo 
low, as to have the weight of many atmofpheres 
over him, no other complaint is recorded, but a 
difagreeable fenfation, as he was defcending, like 
fomething bunding in his ears, and which recurred 
at about the fame depth of water in his afcent. 
From the above obfervations of Dr. halley on 
the fenfation in his ears, when he defcended and 
afcended in the diving-bell, I was led to imagine, 
that the air contained behind the tympanum in the 
veji'ibulum , cochlea , and femicircular canals of the 
ear, had found or made itfelf a way into the Eujla - 
cbian tubes, or into the external ear, by fome un- 
difcovered paffage j and concluded, that a limilar 
operation might be of fervice to fome deaf people, 
where the immediate caufe of their deafnefs might 
be owing to the excefs or defedt of this internal air. 
For this purpofe, a cupping-glafs, which had a 
fyringe to exhauft it, was put over the ears of three 
different 
5 
