one can go in and find the walls thickly
covered with stringy blacks, notably on the gas-pipes and everything
most easily charged by induction. Next fill a bell-jar full of steam,
and electrify, paying attention to insulation of the supply point in
this case. In a few seconds the air looks clear, and turning on a beam
of light we see the globules of water dancing about, no longer fine
and impalpable, but separately visible and rapidly falling. Finally,
make a London fog by burning turpentine and sulphur, adding a little
sulphuric acid, either directly as vapor or indirectly by a trace of
nitric oxide, and then blowing in steam. Electrify, and it soon
becomes clear, although it lakes a little longer than before; and on
removing the bell-jar we find that even the smell of SO2 has
disappeared, and only a little vapor of turpentine remains. Similarly
we can make a Widnes fog by sulphureted hydrogen, chlorine, sulphuric
acid, and a little steam. Probably the steam assists the clearing when
gases have to be dealt with. It may be possible to clear the air of
tunnels by simply discharging electricity into the air--the
electricity being supplied by Holtz machines, driven say by small
turbines--a very handy form of power, difficult to get out of order.
Or possibly some hydro-electric arrangement might be devised for the
locomotive steam to do the work. I even hope to make some impression
on a London fog, discharging from lightning conductors or captive
balloons carrying flames, but it is premature to say anything about
this matter yet. I have, however, cleared a room of smoke very quickly
with a small hand machine.

It will naturally strike you how closely allied these phenomena must
be to the fact of popular science that "thunder clears the air." Ozone
is undoubtedly generated by the flashes, and may have a beneficial
effect, but the dust-coagulating and dust-expelling power of the
electricity has a much more rapid effect, though it may not act till
the cloud is discharged. Consider a cloud electrified slightly; the
mists and clouds in its vicinity begin to coagulate, and go on till
large drops are formed, which may be held up by electrical action, the
drops dancing from one cloud to another and thus forming the very
dense thunder cloud. The coagulation of charged drops increases the
potential, as Prof. Tait points out, until at length--flash--the cloud
is discharged, and the large drops fall in a violent shower. Moreover,
the