184. W. A. Norton— Variability of the Ultimate Molecule. 
sive, or transverse—increasing progressively re a small frae- 
tion of the ee. load, on the removal of the load a certain 
tional to a power of the load which ae more or less, from 
one material to another, and for the same material with the 
ratio of the load to the breaking weight. The law of variation 
falls, in general, between the first and fourth power of the | 
but when the stress is a large fraction of the breaking load, the 
set may increase according to a much more rapid law. This is 
strikingly true of wrought iron 
(2.) There is, strictly speaking, no definite limit of elasticity, 
that is, no minimum limit of the load below which no set results. 
nations, a perceptible set was sain with each material, 
immediately after the stress was removed, heces er small its 
mount, until it fell below the lowest possible determination of 
which the maging was capable (viz: TUsOT of an inch) ; an 
on increasing the delicacy of the measuring apparatas it was 
found that the least pean immediate set was still limited 
only by the capability of detecting, with the apparatus, minute 
——— ts. 
may say, — Aon every load, casigrn small, — 
rise to an immediate s and that the set increases progres- 
sively with the load, sant small the increment of Joad 
m e, up to the point of rupture. If for any ordinary 
material, there is a limiting load below — no immediate set 
results, such limit has not yet been determ 
(3.) ‘The set augments with the dasa of the stress, up t0 
a certain interval of time. When moderate strains are applied 
it has been found that this limiting interval may vary, with the 
strain, from a few minutes to one hour. In experiments with 
subject to raatesiel fluctuations. If very small it may pass 
off entirely in a few minutes. Otherwise, — decreasing 
for a short interval of time (from 5m. to 20m., in the author's 
* By immediate set is meant that which obtains pacers after the stress is 
withdrawn. 
