ON STRENGTH AND PROPERTIES OF CAST IRON. 353 
cast iron, malleable iron, we may therefore assume that it is in 
operation in the crushing of all rigid bodies, and consequently 
that, in any particular one, the resistance will be as the area 
of its section. 
I may perhaps mention that this subject ought to be studied 
in conjunction with optics and crystallization. The singular 
structure of the mineral called analcime, or cubizite, as shown 
by polarized light, and given by Sir David Brewster, Optics, 
chap. xxv., has so much the appearance of some of our frac- 
tures, as to lead one to conceive that it may have arisen from 
compression. 
Transverse strength.—It is to ascertain the resistance of 
materials to a transverse strain that the efforts of experiment- 
ers have chiefly been directed. One reason for this seems 
to be the great facility with which bodies can be broken this 
way comparatively with others, which require large weights or 
complex machinery, and often considerable attention to theo- 
retical requirements. 
In making the following experiments, it has been the au- 
thor’s aim, whilst he kept in view the inquiry respecting hot 
and cold blast iron, to make the results subservient to some 
other purposes, besides giving an extended view of the appli- 
cation of these irons. 
‘ As the inquiry was a comparative one, and required that a 
_ number of experiments, and those similar to each other, should 
_ be made upon each iron from any particular place, several 
models were made, and castings, both of hot and cold blast 
_ iron, obtained from them; and as it seemed desirable to trust 
in these experiments as little as possible to theory, some bars, 
one inch square, were always obtained from the same model. 
From these, and from others, a satisfactory comparison of the 
relative strengths of the irons would have been obtained with- 
out the use of theory, could the castings have always been got 
_ of the exact size of the model; but as small deviations in this 
_ respect were unavoidable, theory was employed to effect the 
slight reduction in the results of each bar to what they would 
_ have been if the bars had been of the exact dimensions of the 
- models. 
__ All the bars used in these comparisons are uniform and of 
_ the same length, and the theoretical assumptions with regard 
_ tothe strength and deflection are of the simplest and most 
_ generally admitted kind. They are as below, the strength in 
_ rectangular bars is taken as the breadth multiplied by the 
_ square of the depth, and the ultimate deflection is supposed 
__ to be inversely as the depth. To these there has been added 
a VOL vi. 1837. QA 
