254 
dynamical, calorimetric or thermometric, see the equations and 
formule given by Clerk Maxwell, Theory of Heat, p. 255. In 
all computations, of a kind where heat is an integral quantity, 
it is assumed that the heat is of a constant temperature, and of 
an even steady flow; where however there is great fluctation, and 
intermittent action: such for instance, as in the case of a burnt 
granite exposed in a conflagration, where the temperature or 
state varies incessantly like the flickering of a candle, it is 
abundantly evident, that the problem becomes of a complicated 
character. In too many problems of the kind, the difficulties 
are eliminated, and so they well deserve the name of “ prepared 
problems ” applied to them. 
A fearful source of danger to the integrity of granite is 
the water locked up in the lacune and pores of its substance. 
On the application of heat, sufficient superheated steam is 
generated, and confined under vast pressures in atmospheres, 
which act as an explosive agent in rending the rock asunder. 
Its force at great pressures is inconceivably great; since it is 
calculated that only one cubic inch of water in becoming steam 
under the ordinary pressure of the atmosphere expands into 1696 
cubic inches, or nearly a cubic foot. And when water is present 
the rise of temperature increases the quantity and density of the 
steam, and hence the elastic force increases in a far more rapid 
proportion. The elastic force of steam in contact with water 
has been lately determined very carefully by Magnus and 
Regnault. The force is expressed in atmospheres; the absolute 
pressure upon any given surface can be easily calculated, by 
allowing 14.6 lb. per square inch to each atmosphere. The 
experiments were carried to twenty-five atmospheres, at which 
point the difficulties and danger became so great as to put a stop 
to the inquiry. So far, some particulars of the structural 
nature of granite, have been presented in a small compass, yet 
sufficient to enable the student to judge for himself, and trace 
the causes and effects into further bearings and relations; so 
extensive and profound are the fields of science into which the 
inquiry would naturally lead the way, that we can barely give a 
glance at them, although intimately connected with the subject : 
