and Strength of Materials. 251 
ratio as before: or that of the compression to 
the extension of the external fibres (since the 
compressions and extensions are here as the 
forces,) and as the ratio remains the same 
for any other degree of flexure, the neutral 
line must, under the conditions of this cor- 
rollary, be fixt. 
PART IL.—Experimental. 
21. In the preceding investigations, the 
theorems, and calculations dependant on 
them, are given in general terms, and seem 
to include all the conditions that can well be 
introduced into inquiries of this nature. But 
before they can be applied to practice, it will 
be necessary to determine, by experiments, 
the values of some of the quantities which 
compose them, as v, ”, 4, &e. where v is 
the power of the extension on which the force 
depends ; w is that of the compression, 
which is in proportion to the power exerted 
to produce it; and a is the distance of the 
neutral line from the extremity of the dilated 
fibres in the surface of fracture. 
EXTENSION. 
92. We will first then spend a few mo- 
ments in considering the subject of exten- 
sion; and as a number of experiments have 
