W. A. Norton — Vuriability of the Ultimate Molecule. 187 
tion as the result of the operation of this force of stress. When 
the load is removed the body should then have a certain set. 
We may add here, incidentally, that all facts and phenomena 
in which imperfect elasticity plays any part (e. g. the prop- 
erties of ductility, malleability and plasticity), are so many 
additional evidences of variations occurring in the mechanical 
state of the molecule. 
second general evidence that the ultimate molecule is 
liable to variation, may be derived from the observed changes 
in the mechanical properties of materials produced by tension, 
pressure, heat, etc. Thus the enacity of iron may be greatly 
increased by wire-drawing, also by hammering and rolling when 
heated. This is generally explained by saying that the parti- 
cles have been brought into new relative positions ; though the 
effect in the latter case is attributed in part to the removal of 
impurities. Such an explanation is little better than a state- 
ment of the fact that a change of configuration bas occurred, 
and the tenacity has in consequence increased. It neither 
states what the change of configuration is, nor why it is possi- 
ble while the inherent forces of the molecules are supposed to 
remain the same, nor why it should be attended with an in- 
crease of tenaci 
tween them. . 
We will add that the well-known effects of tempering and 
annealing, also give intimations of permanent changes effected 
by variations of temperature in the mechanical condition of the 
individual molecules. . ‘ 
Let it not be understood that in what precedes, the intention 
