78 REPORT—1850. 
degree in the exacter branches of cosmical science ; we can show it to be so 
as respects the establishment of the tides, of the great currents of the ocean 
and of the atmosphere, of the relations of land and water to climate, and of 
the astronomical conditions of our planet to its mean temperature; but as 
yet we can only guess from their analogy, as to what and how great may be 
the total effect, of perturbations of climate, and season, and weather, within 
the limits known to us, upon the molecular forces acting beneath the surface 
of the earth, upon which the great agency of elevation depends, and with it 
the volcano and the earthquake. 
But again, we may view it thus: granting that perturbations of climate, 
season and weather, may not be the appointed agents in determining the 
local play of the all-present force of elevation, may it not be that their dis- 
turbance may be the sufficient and immediately anterior cause, of their being 
brought into play within a given region, where before they were in equili- 
brium, but nearly ready to break forth; the last drop as it were to cause the 
cup to flow over? 
To take (in our ignorance) a rude example ; suppose a widely-extended tract 
of sea-bottom, beneath one portion of which, or of adjacent land, the ignited 
or fluid materials of the inner earth have approached the surface by thin- 
ning of the solid crust, or in a word, by any such play of forces as have 
been well imagined by Mr. Babbage and Sir J. Herschel. Let this portion 
be under the dry land; and suppose the ordinary rise and fall of tide at the 
place to be 15 feet or so, that by any of the combined causes which are 
known to affect the local establishment of tides this becomes a 20-fvot tide, 
and that at the same time a rise of 2 inches of the barometer takes place 
over the sea, and a corresponding fall over the land. The conspiring 
effeet of all this would be equivalent to a tide of about 80 feet in total 
rise, brought at once to bear upon the already thinned crust of sea- 
bottom ; this, taking the specifie gravity of fluid and porous lava at about 
2:0, being equal to a bed of this of 40 feet in thickness, or to a dead 
pressure of nearly 20 tons per square yard, and acting over hundreds of 
square miles of surface, it is conceivable that the combination of cireum- 
stances might at once bring on an active eruption and earthquake, felt far 
away upon the land, which otherwise had reposed in safety on its molten 
base. Compare Von Buch, ‘ Descript. des [les Canar.’, p. 334, and Hoffman, 
in Poggendorff’s Annalen, band xxiv. s. 8. 
Nor yet may the changes in the organic world of life upon the earth be 
without influence upon these, the most formidable forces that exhibit them- 
selves in nature. Who has yet determined, for example, what meteorological 
effect is produced, by the wonderful change that takes place during the year 
in the vegetable covering, upon the surface of the plains of the Pampas, 
where over thousands of square miles of country covered with scorched and 
embrowned grass and lowly herbage, a forest of gigantic thistles grows up, 
and in a few weeks makes the plain impassable for man or beast, and the 
earth no longer reached by the sun’s rays? What may be the co-exercitive 
effect within the tropics of the changes of the vegetable world at the com- 
mencement and end of the rainy season, at the vernal and autumnal equi- 
noxes, and at the changes of the monsoons, at which times popular belief. 
has long asserted within the tropics some connexion with earthquake? and 
long-held popular belief usually contains some deformed truth, misinter- 
preted and overlaid with a mass of error, but yet a truth within. 
On this branch of our subject we literally know nothing; and in the obser- 
vations upon it just concluded, 1 have been anxious rather to suggest the 
directions in which future investigation may run, than to advance any con- 
nected speculations where there is at present no certain basis for them. 
ie 
