404 PHILOSOPHICAL TRANSACTIONS. [aNNO I67O. 



from the lowermost part of the atmosphere, as to exclude certain steams of a 

 peculiar nature, which in some places the air may be imbued with ? In favour 

 of which suspicion I remember, that inquiring once of an intelligent man, who 

 had lived several years in the island of TenerifFe, whether he had been at the 

 top of the Peak of that name, and what he had there taken notice of about the 

 air? he answered me, that he had attempted to go up to the top of the moun- 

 tain, but that though some of the company were able to do so, he and some 

 others before they had reached near so high, grew so sick upon the operation 

 they felt of the sharp air, and sulphureous exhalations which infected it, that 

 they were forced to stay behind their companions, he having already found this 

 effect of those piercing steams upon his face (which when he made me this re- 

 lation was of a fair complexion) that the skin began to be of a pale yellow, and 

 even his hair to be discoloured. 



The Twelfth Title. 



Of the Observations produced in an Animal in Changes as to Rarity and Density/ 



made in the self-same Air. 



In the experiments hitherto recited, the animals that were recovered from a 

 gasping condition, have been so by letting in fresh air upon them, and not the 

 same that had been withdrawn from them. Wherefore I thought it very re- 

 quisite to try, whether the same portion of air, without being renewed, would, 

 by being expanded much beyond its usual degree, and reduced to it, serve to 

 bring an animal to death's door, and revive him again; since by the success of 

 such a trial, it would notably appear, that the bare change of the consistence of 

 the air, as to rarity and density, may suffice to produce the above-mentioned 

 effects. 



But to devise a way to put this experiment in practice appeared no easy mat- 

 ter; since it required a receiver that should be transparent, and be capable of 

 changing its bulk without suffering any air to get in or out. 



To surmount these difficulties, the first thing I thought on was, to take a 

 fine clear bladder of a sheep or hog, made more transparent by being anointed 

 with oil, which was done on the outside, that the smell of it might less offend 

 the animal to be included. Then we clipped off as much of the bladder at the 

 neck, as was judged absolutely necessary to make an orifice capable of letting 

 in a mouse ; that sort of animals being, by reason of their smallness, the fittest 

 of those furnished with lungs and hot blood we could procure. And whereas 

 it seemed very difficult, when the neck of the bladder was cut off, to make up 

 so large an orifice without wrinkles, at which the rarefied air may escape ; to 

 Dbviate this inconvenience, we provided a round stick somewhat less than the 



