348 SEVENTH REPORT—1837. 
the prism; this wedge has, commencing at its vertex C, a 
sharp line C D, { inch long; and by the operation of its sides, 
the wedge has removed the parts E. and F, and separated the 
sides G and H, which before joined together at the top and 
formed part of the upper side of the prism. The part AB, 
adhering to the lower part of the wedge, and which had 
formed part of the side-of the prism, was nearly separated by 
the action of another wedge formed by the lower end of the 
part G, which formed a wedge not represented by the 
figure, but whose vertex formed a sharp line about ‘43 inch 
long in the direction IK. This wedge occupied the space 
between B and C D, and its tendency was to split off from the 
principal wedge the only remaining portion A B. 
Fig 21 represents a prism of the form of an equilateral 
triangle, and fig. 22 is its appearance after fracture. ‘The 
tendency is here, as before, for opposite wedges to be formed, 
which split off the angles and separate the sides. Figs. 23, 
24, 25, give direct representations of the three sides. 
Angle of Wedge.—We have seen that when bodies are 
subjected to a crushing force, their fracture, if they do not 
break by bending, is caused by the operation of a cone or 
wedge, which seems, under various circumstances, to slide off 
at nearly aconstant angle. Ifa prismatic body, as for instance 
a short cylinder, be subjected to a crushing force, there 
seems no reason why fracture should take place one way more 
than another; there is usually too in soft irons a bulging out 
in every direction round the cylinder, which shows that it is 
equally strained all round: a matter which is otherwise exem- 
plified in fig. 8. If then the cylinder be longer than the wedge, 
or than the two cones which are always in operation at the 
ends during crushing, it is evident that the angle of the wedge 
and cones, which is the same, will depend upon the nature of 
the material, and the cones must be isosceles. Cylinders 
longer than the wedge usually slide off in one direction with- 
out showing the cones, but some examples in other forms 
have been obtained; as for instance, in the fracture of a rect- 
angular specimen whose base was 1°00x°26, and its height 
50 inch (Table I.), the rupture took place by wedges, which 
appeared to be isosceles, being formed at the top and bottom 
of the ends of the specimen, and dividing the sides in the 
middle, (as in the fig. -) 
In cases however where the height of the specimen was not 
