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I fifld this fet down among my Ad verfaria • t/l^.p ^Ifa inquired of him 
whether they found the Air at the Top as fit for Refpiration as Com- 
mon Air, which he told me they did not, but were fain to breath flior- 
ter,and oftner than ufuall and becaufe I fufpeded , that might come 
from their motion,! askM,whether they obfervM it to ceafe, when they 
came down to the Bottom of the HiH,which he told me they plainly did, 
befidcs that they llayM many hours at the Top, too long to continue out 
of Breath. 
But that! may not here conceal anything, that may conduce to the 
Difcovery of the truth in the matter under confideration, I fliali here 
add, that I did fometimcs think it worth further Inquiry, Whether the 
Sicknef5,if not alfo the Difficulty of breathing, that fome have been ob» 
noxious to in the uppermoft parts oi Pdriacacha, and perhaps fome other 
high Mountains, may not be imputed not fo precifely to the Thinnefs 
and Rarity of the Air in places fo remote from the lowermoO; part of 
" the Atmofphere^as to exclude certain fleams of a peculiar nature^ which 
in fome places the Air may be imbued with ? In favour of which fufpi=- 
tion I remember, that inquiring once of an intelligent man, who had 
liv'd feveral years in the Ifland of Tenerijfe.^htih^ic he had been at the 
Top of the P/rof that name, and what he had there taken notice of about 
^the Air ? He anfwer'd me,That he had attempted to go up to the Top of 
the Mountain, but that, though fome of the Company were able to do fo^ 
he and fome others, before they had reached near fo high, grew fofick 
upon the operation they felt ofiheHiarp Air, and Sulphureous exhalati- 
ous which infefted it, that they were fain to flay behind their Compa- 
nionsjhe having already founa this eifed of thofe piercing fleams upon 
his face (which when he made me this relation, was of a fair complexion) 
that the skin began to be of a pale-yellow, and even his hair to be dif- 
colour'd. 
The XII. Title. 
Of the Oh fervAttons produced in m Animd in Changes as to Rarity MdDen^ 
JitymiideintheM^-hmtAir. 
In the Experiments hitherto recited,thc Animals that were recovered 
from a gafping Condition, have been fo, by letting in frclh Air upon 
them, and not the fame that had been withdrawn from them. Wherefore 
I thought it very requifite to try. Whether the fame portion of Air, 
wi-thout being renew'd, would, by being expanded much beyond its ufu- 
al degree, and reduced to it, fcrve to bring an Animal to Deaths door, 
sind revive him again • fince by the fuccefsof fuch a Tryal,it would no- 
tably appear, that the bare change of the confidence of the Air, as to 
Rarity and Denfity, may fuffice to produce the abovcmentioned Ef- 
But to devifc a way to put this Experiment in pradice app ar'd no 
cafy matter^ fince it required a Receiver thar fhould be tranfparentg 
& be capable of changing its bulk without fuffcring any Air to get in 
€r out. 
To 
