SECTION II.

_An account of the APPARATUS with which the following experiments were
made._

Rather than describe at large the manner in which every particular
experiment that I shall have occasion to recite was made, which would
both be very tedious, and require an unnecessary multiplicity of
drawings, I think it more adviseable to give, at one view, an account of
all my apparatus and instruments, or at least of every thing that can
require a description, and of all the different operations and processes
in which I employ them.

It will be seen that my apparatus for experiments on air is, in fact,
nothing more than the apparatus of Dr. Hales, Dr. Brownrigg, and Mr.
Cavendish, diversified, and made a little more simple. Yet
notwithstanding the simplicity of this apparatus, and the ease with
which all the operations are conducted, I would not have any person, who
is altogether without experience, to imagine that he shall be able to
select any of the following experiments, and immediately perform it,
without difficulty or blundering. It is known to all persons who are
conversant in experimental philosophy, that there are many little
attentions and precautions necessary to be observed in the conducting of
experiments, which cannot well be described in words, but which it is
needless to describe, since practice will necessarily suggest them;
though, like all other arts in which the hands and fingers are made use
of, it is only _much practice_ that can enable a person to go through
complex experiments, of this or any other kind, with ease and readiness.

For experiments in which air will bear to be confined by water, I first
used an oblong trough made of earthen ware, as _a_ fig. 1. about eight
inches deep, at one end of which I put thin flat stones, _b. b._ about
an inch, or half an inch, under the water, using more or fewer of them
according to the quantity of water in the trough. But I have since found
it more convenient to use a larger wooden trough, of the same general
shape, eleven inches deep, two feet long, and 1-1/2 wide, with a shelf
about an inch lower than the top, instead of the flat stones
above-mentioned. This trough being larger than the former, I have no
occasion to make provision for the water being higher or lower, the bulk
of a jar or two not making so great a difference as did before.

The several kinds of air I usually keep in _cylindrical jars_, as _c_,
_c_, fig. 1, about ten inches long,