XXVI. W. H. WARREN. 
The strength of cubes placed one on the other varies with the 
number of cubes, thus: for one, two and three cubes Rondelet 
found in one series the strengths to be 1 : 0°61 : 0°5 respectively, 
in another series 1 : 0-80 : 0°75 respectively. 
In tension, compression, and transverse tests made on ductile 
materials there are three successive changes of state more or less 
clearly defined, which mark the limit of elasticity, the commence- 
ment of the plastic period, and the limit of cohesion or completion 
of the plastic period. The first.change shows itself in tension 
tests and in compression tests, when the pieces are sufficiently 
long, by the elongations or shortenings of the specimen ceasing to 
be proportional to the loads producing them, and by the disappear- 
ance of the deformations when the loads are released. In trans- 
verse tests of beams the first change is marked in a similar manner 
by the deflections ceasing to be proportional to the loads producing 
them. 
The second state is marked in tension and in transverse tests 
by the commencement of the permanent elongations, and deflec- 
tions respectively ; but in compression tests this change is shown 
by the commencement of the swelling of the piece in the form of 
a barrel, termed by the French refoulement. It is not necessarily 
however, the limit of cohesion. In order that it may be developed 
in the test piece the length must not greatly exceed the diameter 
or buckling will be produced. 
The third change marking the limit of cohesion is shown in 
tension by the rupture of the specimen, in transverse tests of 
beams also by rupture, unless the material is so soft and ductile 
as in some kinds of mild steel, that the beams fail to support 
the loads by bending. In compression of short pieces the third 
change is shown by a decided swelling of the piece, although the 
load is perfectly supported. 
The following shows the details on one of the tests made by 
Prof. Tetmaier on ingot iron, and is given as a specimen sheet for 
recording the results made to determine the relative elastic com 
pression coefficients. 
