[ 23.8 ] 
tions, and their manner of operating upon - the hu- 
man body, may receive ample fatisfa^ion from Boyle 
in his treatife of Effluvia. The fagacious Helmont, 
therefore, very judicioufly recommends a more fre« 
quent ufe of thofe furious incoercible fpirits, and vo- 
latile fumes, in the practice of phyfic ; juffly obferving 
that no other medicines operate fo fuddenly and fo 
powerfully upon the human body (4). 
Neither ought we^ becaufe thofe fpirits of fountains' 
are flatulent and elaflic, from thence to infer, that 
they agree with common air in every other refpedl, 
as many are apt to imagine. For corpufcles, which 
differ extremely in magnitude, denfity, and figure,- 
may all be endowed with one common repulfive 
quality. And it is highly probable that the elafiiic 
particles, which are emitted from various kinds of 
denfe bodies, do thus vary one from another ; and 
that they oft-times compofe elaffic fluids, which differ 
as mucli from each other, as thofe bodies differ from 
which they are produced. Thus the air of peafe, 
which is inflammable, feems to differ as much from 
the mephitical air of oak, which* cxtinguifhes flame, 
as thofe two vegetable fubffances difler between 
themfelves. So that two elaftic fluids, altho’ they 
both poffefs a repulfive quality, may yet in their other 
qualities differ as much as inelaftic fluids are found 
to differ i as water, for example, differs from oil of 
vitriol. The particles, therefore, of denfe bodies, 
when they are feparated from each other, and affume 
a repulfive quality, are not always reduced to com- 
mon air, but to different kinds of elaftic fluids, 
(4) In the preceding Eflays on the Fulminating-damp, and 
the (Jhoak-damp. 
wliich 
