35 
This experiment was attended with considerable difficulty, 
as the moisture from the steam seemed to get on to the glass 
shade over the gold leaves and so form a charged conductor 
between the leaves and cloud. The cloud was first formed 
by a jet of steam from a pipe, then by the vapour from a vessel 
of boiling water, and lastly by a smoke ring or rather a steam 
ring. By this latter method an insulated cloud was formed* 
which, as it passed was attracted by the charged leaf. 
Of the two latter propositions I have not been able to 
obtain any experimental proof. I made an attempt, but 
failed, through the bursting of the vessel in which the cloud 
was to be formed. I hope, however, shortly to be able to 
renew the attempt, and in the meantime I will take it for 
granted that these propositions are true. Faraday main- 
tained that evaporation was not attended by electrical 
separation unless the vapour was driven against some solid 
when the friction of the particles of water gave rise to elec- 
tricity. So that unless there were some free electricity in 
the steam or vapour before it was condensed none could be 
produced by the condensation, and hence the cloud when 
formed would be uncharged. 
In the same way with regard to evaporation, unless, as is 
very improbable, the steam into which the water is turned 
retains the electricity which was previously in the condensed 
vapour ; the electricity from that part of the cloud which 
evaporates must be left to increase the tension of the re- 
mainder. So that, as a charged cloud is diminished by 
evaporation the tension of the charge will increase, although 
the charge remains the same. 
I will now point out what I think to be the bearing which 
these propositions have on the explanation of thunder storms. 
In doing this, I am met with a great difficulty, namely ? 
ignorance of what actually goes on in a thunder storm. We 
seem to have no knowledge of any laws relating to these 
every-day phenomena ; in fact we are where Franklin left 
