give the same
differences. It has been already noticed that the negative numbers are
lower than the positive (1393.), but, besides that, the _order_ of the
positive and negative results is not the same. Thus, on comparing the mean
numbers (which represent for the present insulating tension,) it appears
that in air, hydrogen, carbonic acid, olefiant gas and muriatic acid, the
tension rose higher when the smaller ball was made positive than when
rendered negative, whilst in oxygen, nitrogen, and coal gas, the reverse
was the case. Now though the numbers cannot be trusted as exact, and though
air, oxygen, and nitrogen should probably be on the same side, yet some of
the results, as, for instance, those with muriatic acid, fully show a
peculiar relation and difference amongst gases in this respect. This was
further proved by making the interval in air 0.8 of an inch whilst muriatic
acid gas was in the vessel _a_; for on charging the small balls _s_ and S
positively, _all_ the discharge took place through the _air_; but on
charging them negatively, _all_ the discharge took place through the
_muriatic acid gas_.

1400. So also, when the conductor _n_ was connected _only_ with the
muriatic acid gas apparatus, it was found that the discharge was more
facile when the small ball _s_ was negative than when positive; for in the
latter case, much of the electricity passed off as brush discharge through
the air from the connecting wire _p_ but in the former case, it all seemed
to go through the muriatic acid.

1401. The consideration, however, of positive and negative discharge across
air and other gases will be resumed in the further part of this, or in the
next paper (1465. 1525.).

1402. Here for the present I must leave this part of the subject, which had
for its object only to observe how far gases agreed or differed as to their
power of retaining a charge on bodies acting by induction through them. All
the results conspire to show that Induction is an action of contiguous
molecules (1295. &c.); but besides confirming this, the first principle
placed for proof in the present inquiry, they greatly assist in developing
the specific properties of each gaseous dielectric, at the same time
showing that further and extensive experimental investigation is necessary,
and holding out the promise of new discovery as the reward of the labour
required.

* * * * *

1403. When we pass from the consideration