448  M. G. Wertheim on the Cubical Compressibility 
experiment by means of a method susceptible of almost any 
degree of accuracy, that this ratio was really 4. Subsequent 
experiments, less direct, but made on a greater variety of bodies; 
have confirmed this result. 
These researches have given rise to numerous discussions. 
Several distinguished geometricians, without repeating my expe- 
riments, and without disputing their accuracy, have endeavoured 
to bring them into accordance with the ancient theory by vari- 
ous and, unfortunately also, very arbitrary hypotheses. I shall 
shortly mention and discuss these hypotheses before describing 
my new experiments on this subject. 
In a memoir published shortly after mine, M. Clausius ex- 
pressly acknowledged that the bodies on which I had experi- 
mented may be considered as truly homogeneous and isotropic ; 
but he thinks that the secondary elasticity discovered by M. 
Weber in silk threads, and which I have observed in several 
organic bodies, may serve to explain this disagreement between 
experiment and the ancient theory. This secondary action being 
added to the true or primary elongation, will give rise to an ex- 
cessive actual elongation, the numerator of the fraction being 
thus increased to such a degree that, though really equal to + 
when only the primary elongation is considered, it in fact ap- 
proximates to Z. 
Against this explanation it may be objected, in the first place, 
that it is founded on a fact absolutely hypothetical, no one ~ 
having yet observed this secondary action either in metals or in 
glass, which are the only bodies I experimented on. Some ex- 
periments of M. Weber are, it is true, appealed to, according to 
which the transverse note produced by a metallic wire which has 
been suddenly stretched, becomes lower for several seconds. 
Seebeck has in fact endeavoured to explain this phenomenon on 
the ground of the secondary action above mentioned—contrary, 
however, to the very plausible opmion of M. Weber himself, who 
attributes it solely to the diminution of the temperature of the 
wire produced by its elongation, and its gradual return to the 
temperature of the surrounding atmosphere. But even admit- 
ting the hypothesis of M. Seebeck, this lowering of the note 
is at all events far too small for its corresponding secondary 
elongation to account for the numerical result of my experiments ; 
and M. Clausius is therefore obliged to suppose that, in the case 
of metals, this species of elongation principally takes place during 
the first quarter of a second, and consequently produces no sen- 
sible effect on the note. But the primary action itself not being 
instantaneous, how is it possible to fix the limit of time beyond 
which the effect ought to be considered as secondary? Itis thus 
that hypotheses accumulate. 
