cribed in his beautiful and
important investigations contained in the Philosophical Transactions;
namely that induction is the same in rare and dense air, and that the
divergence of an electrometer under such variations of the air continues
the same, provided no electricity pass away from it. The effect is one
entirely independent of that power which dense air has of causing a higher
charge to be _retained_ upon the surface of conductors in it than can be
retained by the same conductors in rare air; a point I propose considering
hereafter.

[A] Philosophical Transactions, 1834, pp. 223, 224, 237, 244.

1288. I then compared _hot and cold air_ together, by raising the
temperature of one of the inductive apparatus as high as it could be
without injury, and then dividing charges between it and the other
apparatus containing cold air. The temperatures were about 50 deg. and 200 deg.,
Still the power or capacity appeared to be unchanged; and when I
endeavoured to vary the experiment, by charging a cold apparatus and then
warming it by a spirit lamp, I could obtain no proof that the inductive
capacity underwent any alteration.

1289. I compared _damp and dry air_ together, but could find no difference
in the results.

* * * * *

1290. _Gases._--A very long series of experiments was then undertaken for
the purpose of comparing _different gases_ one with another. They were all
found to insulate well, except such as acted on the shell-lac of the
supporting stem; these were chlorine, ammonia, and muriatic acid. They were
all dried by appropriate means before being introduced into the apparatus.
It would have been sufficient to have compared each with air; but, in
consequence of the striking result which came out, namely, that _all had
the same power of_ or _capacity for_, sustaining induction through them,
(which perhaps might have been expected after it was found that no
variation of density or pressure produced any effect,) I was induced to
compare them, experimentally, two and two in various ways, that no
difference might escape me, and that the sameness of result might stand in
full opposition to the contrast of property, composition, and condition
which the gases themselves presented.

1291. The experiments were made upon the following pairs of gases.

1. Nitrogen and Oxygen.
2. Oxygen Air.
3. Hydrogen Air.
4. Muriatic acid gas Air.
5. Oxygen