[ 55 ] 
Wherefore it cannot be doubted, that this vapoiir 
is capable of taking away the life of an animal. If 
experiments had dilcover’d to us any peftilential qua- 
lity, any fecret poifon in it, doubtlefs we ought, 
with moft authors, who have treated of mof eta’s , to 
range it among thofe deadly exhalations, whofe bad 
effects are felt, before they can be forefeen ; becaufe 
they do not ftrike our fenfes by any difagreeable 
fmell, or any other quality proper to infpire miftruft. 
But it is not by the bare extinction of animal life, that 
ajudgment can be formed of them, inafmuch as this 
effeCt may equally proceed, either from a fubftance, 
that aCts by deftroying or infeCting as a poifon ; or 
from a fluid, which takes the place of another, whofe 
functions it is not capable of performing. It is rather 
by examing the vapour itfelf, with a view to know its 
nature, or at leaf! fome of its effential qualities ; and 
in this view it was that I profecuted my experiments. 
Having cut a fheet of blue paper in two, I laid 
one half of it on the ground in the grotto, and let it 
it lie there near half an hour. When I took it out, it 
was fomewhat warm, it had contracted no moiffure, 
and its colour, compared with that of the other half- 
fheet, which I kept in my pocket, underwent no 
other change than a flight caft inclining to violet. 
I placed a water-glafs, with the mouth down- 
ward, at the bottom of the grotto, and left it in 
that fltuation long enough to have reafon to think r 
that the vapour had well filled it. I then turn’d it, 
and fet it on its bottom, without taking it out of the 
vapour, and then poured fome fyrup of violets into it, 
but I could not perceive any change, of colour in the 
fyrup. 
The 
