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The Air, in Ships particularly, is very liable to be 
vitiated; not only from the Bulge- water, but from 
too many People breathing in the fame Atmofphere ; 
efpecially in Ships of War, Hofpital-fhips, and thofe 
ufed in the Guinea Trade for Negroes , where a Num- 
ber of uncleanly People, being flowed too clofe to- 
gether, heat the Air, make it replete with noxious 
Effluvia , deftroy the Particles therein adapted to cool 
the Lungs, particularly the acid nitrous Gas , which 
is fo abundant in cool Air, and manifefts itfelf not 
only from the Quantity of nitrous Cryflallizations, 
which may be colleded from Caverns of the Earth, 
efpecially thofe open to a Northerly Afped, but from 
expofing Pieces of the Flefh of Animals frelh cut, or 
their Blood, whereby the Colours of their Surfaces 
are foon changed from a dark deep Red to a more 
lively and florid one. Air robbed of this valuable 
Property, and replete with hurtful ones, not only 
from the People, but from the (linking Water in the 
Well and lower Parts of the Ship, muft produce the 
rnoft putrid, if not peftilential Fevers. 
Although the ^^/Equilibrium within Places confined 
is maintained by the external Air, yet unlefs, by 
Openings properly adapted, the Air is fuffered to pafs 
freely through, the external Air proves as a Stopple 
to the internal, and only mixes with the next in 
Contad; as is evident from the common Occurrence 
in Privies, which are fcarcely offenfive in clear Wea- 
ther, but are much fo in foul or windy, from a Di- 
minution of the incumbent Prefliire, when the Va- 
pours that have been pent up, expand themfelves to a 
confiderable Diftance. 
To 
