238 On the Transverse Strain, 
rection of GW, parallel to the surface of 
fracture adbc, can have no influence in 
pushing the piece toward or drawing it from 
the wall : and therefore the pressure on the 
fulcrum f must just be as great as the resist- 
ance in F, all the horizontal forces being 
supposed collected into those two points. 
For the first outline of this subject, see the 
valuable treatise of Dr. Robison, referred to 
above. 
15. Example. To find the strength of a 
rectangular beam, broke by a weight at the 
end as before ; the situation of the neutral 
line being given. 
x Pf= twice the forces in F X PF. The mode of es- 
timating the strengths of bodies, as deduced from this, is 
very simple and easy ; it is in effect this :—Find the neu- 
tral line—suppose éhat the fulcram—estimate the strength 
of the area of tension, as was done in incompressible 
bodies, and double that for the answer. 
But this rule, it appears to me, contains within itself a 
fundamental error which will become very apparent by the 
following consideration.—It is supposed tobe general what- 
ever the situation of the neutral line may be. Let then the 
body be incompressible; the neutral line will in that case 
be extremely near the edge, and the strength as estimated 
by this rule will be double what from incontestable prin- 
ciples it ought to be: a consequence which the ingenious 
author could have had no idea of when he proposed this 
theory. The error too will be found to exist, though in a 
less degree, in almost every other position of the neutral 
