OF THE IRK, LOCOMOTIVE ENGINE. 517 
It is supposed, that the force, by which the Engine was 
disengaged from the tender, was equal to that which would 
break two beams. 
12. To show in what manner the modulus of 
elasticity is limited by the modulus of rupture, in 
the Tables in Mr. Moseley’s Engineering, &c. 
E=the weight, in pounds, which would be required to extend 
a beam, whose section is one square inch, and whose 
length is one foot, to the length of two feet ; and, 
S=the weight, in pounds, which, at the section of rupture, is 
just equal to the force of extension of a beam, whose 
section is one square inch, and whose length is one foot. 
Tn using the modulus of elasticity, E, it is supposed, that 
the beam, whose section is one square inch, may be extended 
to twice its length without breaking, and that, during the whole 
of this extension, its elasticity may remain perfect ; but, this 
supposition is limited by the use of the modulus of rupture, 8. 
For, let A=the extension, by the weight, S, of a beam, 
whose section is one square inch, and whose length is L feet ; 
then, E: L:: S: a; or, 
Ss a da! e : F : ° 
wo 4 adopting Mr. Moseley’s Notation, in 
his Engineering, &e. Art. 357, and observing, that, in this 
case, dz' is the greatest extension, of which the fibre, whose 
OZ 
