nic vents. 2. The evolution of steam and
other heated elastic fluids by which these are carried. 3. The work of
raising through a certain height all the materials ejected. To which we
must add a large allowance for waste, or thermal mechanical and chemical
energy ineffectually dissipated in and above the vents. All these are
measurable into units of heat.

I have applied this method of calculation to test the adequacy of the
source I have assigned for volcanic heat, in two ways, viz.: 1. To the
phenomena presented during the last two thousand years by Vesuvius, the
best known Volcano in the world; and 2. To the whole of the four hundred
and odd volcanic cones observed so far upon our globe, of which not more
than one-half have ever been known in activity.

It is impossible here to refer to the details of the method or steps of
these calculations. The result however is, that making large allowances
for presumably defective data, _less than one-fourth_ of the total
telluric heat annually dissipated (as already stated in amount) is
sufficient to account for the annual volcanic energy at present expended
by our globe.

It is thus represented by the transformation into heat of the work of
crushing about 247 cubic miles of (mean) rock, a quantity so perfectly
insignificant, as compared with the volume of the globe itself, as to be
absolutely inappreciable in any way but by calculation; and as its
mechanical result is only the vertical transposition transitorily of
material within or upon our globe, the proportion of the mass of which
to the whole is equally insignificant, so not likely in any way to
produce changes recognisable by the astronomer.

Space here forbids my entering at all upon that branch of my
investigation which is based upon the experimental results, above
mentioned, of the total contraction of fused rocks: for these, the
original Paper can, I hope, be hereafter referred to. I am enabled,
however, to prove thus how enormously more than needful has been the
store of energy dissipated since our globe was wholly a melted mass, for
the production, through the contraction of its volume, of all the
phenomena of elevation and of Vulcanicity which its surface presents.
And how very small is the amount of that energy in a unit of time as now
operative, when compared with the same at very remote epochs in our
planet's history.

I have said that if we can find a true cause in Nature for the
origination of volcanic