IN BEAMS SUBJECTED TO TRANSVERSE STRAIN. 
231 
The force acting when F is the strain which breaks the outer fibre, will be 
Hence 
cf X 2 — 3 ( d-\- 
or 
W= 
The value of W being obtained by experiment in each case, we have from tlie for- 
mula 
3/W 
F= 
2a{d + c + ‘-^ 
and if the strength depended only on the direct tensile power of the material, F 
should in each case be constant, and equal to the direct tensile resistance ; but if, in 
addition to this, there existed another element of strength in the resistance occa- 
sioned by the lateral adhesion and varying with the flexure, the value of F would be 
found, in every case, greater than the tensile resistance, and to increase when the 
flexure increased. 
Four beams were cast of each form, of which the details, the exact dimensions, 
deflections, and breaking weights are given in the Appendix. The results were as 
follows, obtained from the mean of four experiments on each form of girder : — 
Description of beam. 
Total depth of 
beam. 
Sectional area 
of the two ribs. 
Distance between 
the ribs. 
Deflection with 
nine-tenths of 
breaking weight. 
Breaking 
weight. 
in. 
in. 
in. 
in. 
lbs. 
Form No. 2 
2-51 
1-98 
•54 
•510 
2468 
Form No. 3 
3-00 
2-00 
1-00 
•401 
3119 
Form No. 4 
4-00 
1-98 
2*03 
•301 
4339 
The value of F being derived from each of these results by the formula 
sm 
Deflection. 
Value of F. 
Form No. 2 
•510 
35386 
Form No. 3 
•401 
31977 
Form No. 4 
•301 
28032 
The tensile strength of the metal obtained from the mean of eight experiments, 
given in the Appendix, was 18,750 lbs. ; here, therefore, was decided evidence, first, 
that the value of F exceeded the tensile strength in all three forms, and that it in- 
creased with the increase of flexure. 
