138 
Proceedings of the Royal Society 
The disturbance has, in fact, its origin above the lower stratum, 
and works its way downwards into it. 
It is also competent to explain the production of similar rotat- 
ing storms in the higher regions of the atmosphere — many miles 
above the earth’s surface — and thus to account for that by no 
means small number of cases of so-called “ summer-lightning,” 
which obviously cannot be explained by the occurrence of an ordi- 
nary thunderstorm at such a distance as to be below the specta- 
tor’s horizon. 
I have already explained to the Society that a possible source of 
at least a large part of the electric charge of a thunder-cloud is 
the contact-electricity of water-vapour and air. Thus while the 
precipitation of the vapour develops heat, the water particles pre- 
cipitated are strongly electrified. And the aggregation into one 
of a number of equal little drops all charged to the same potential 
may increase the potential in any ratio whatever. Thus the 
charge on each drop in a large cloud may become so great that the 
electricity is driven entirely to the particles at its surface. This 
is supplementary to, and does not interfere with, Sir W. Thomson’s 
explanation of the process by which the vapour is condensed. 
It is possible that taking place in greatly larger spaces of air, 
but to a much smaller extent in each cubic foot, this sudden pro- 
duction, and as sudden scattering in all directions, of considerable 
quantities of electricity, may account for some of the main pheno- 
mena of the Aurora. 
3. An Application of Professor James Thomson’s Integrator 
to harmonic Analyses of Meteorological, Tidal, and other 
Phenomena, and to the Integration of Differential Equa- 
tions. By Sir W. Thomson. 
A first rough Model of Professor J. Thomson’s Integrator was 
shown. 
4. Note on the Thermo-Electric Position of Cobalt. By 
Professor Tait, 
