Dr. Fothergill’s account of ice islands. rR 
been found to exceed 53° that the most combustible materials con- 
tained in the bowels of the earth impart no sensible heat to the neigh- 
bouring strata till they are decomposed, and then probably may give 
rise to warm springs. Nor does a mass of gunpowder emit any heat 
till the moment of explosion. But effects of this nature are merely 
local, transitory, and circumscribed. 
Besides, the received notion of central fire is entirely hypothetical, 
and apparently groundless, for hot and cold springs often issue from 
the same hill, and volcanoes have been known to burst forth from 
mountains covered with snow. The native heat oh the Fat and 
ocean then seems to be derived from a more steady, ETT 
dependent solely on the sun, whose enlivening rays cheer all n nature. 
Were this source of heat totally withdrawn, all our rivers and the 
ocean itself would probably soon be converted into ice. | Water by 
the mere absence of a certain portion of heat assumes a solid, crystal- 
line form. | Hence, by means of artificial cold, ice may be formed in 
the hot regions 0 of sd torrid ig Sane also in n the frozen polar 
* The Reltunled & cavern of Grace Dieu in Woaentone 146 feet ander pround, 
presents a singular and curious phenomenon. Witbin it in summer ice is form- 
ed in large quantities, and this ice diminishes at the approach of winter. “ The 
air within,” says M. Cc. Cadet, “ did not feel colder to me, than that of the open at- 
mosphere ; nor does the water, which filters into ‘it, freeze as it falls into a cavity, 
formed below in the ice ; neither does the water seem very cold, when drank.” 
As no natural philosopher has yet been able to explain this interesting phenome- 
non, he conjectures that the abundant aqueous evaporation of the bushy trees; 
with which it is surrounded, cooling the earth and air around the cavern during 
summer, tends to produce this effect, till they drop their foliage, when the cooling 
i deh of Hepes: ceases. He thinks it somewhat similar to the ae. of 
a}. ah 
in hot countries, by means of water 
"Annales de Chimie 1808; p- 160. 
10 
