THE CONTACT OF BODIES HAVING DIFFERENT TEMPERATURES. 
9 
occur when rocker and bearer are of the same metal. The same facts deprive the 
latter part of the third law of its significance. 
I will however cite one or two experiments, in which the conditions regarded 
necessary by Professor Forbes were reversed, and the effect was produced notwith- 
standing. 
1. Silver stands at the head of the conductors of heat. A copper rocker was laid 
upon the edge of a thin plate of this metal; strong musical notes were obtained from 
the arrangement. 
2. Forcible vibrations were produced by placing a brass rocker upon the same 
silver plate. 
3. A feehle, but distinct tone, was produced by the iron rocker. 
4. Gold is a better conductor than brass ; nevertheless strong vibrations were 
obtained by placing a hot brass rocker upon the edge of a half-sovereign. 
These experiments are, I think, sufficient to prove the non-existence of the third law. 
In the prosecution of his inquiry Professor Forbes discovered “ that at least two 
metals were perfectly inert in either situation, namely, antimony and bismuth.” 
Considering the explanation given, that the effects are due to the mechanical repul- 
sion exerted by the heat in its passage from a good conductor to a bad one, the 
inertness of the two bodies mentioned presents a grave difficulty. Reflecting on the 
subject, the thought occurred to me, that if a mass of bismuth or antimony were cut 
so that the plane of most eminent cleavage might be vertical, the superior conduct- 
ivity which the mass probably possesses in the direction of the said cleavage might 
aid in the production of the vibrations. I cut such a piece from a mass of antimony 
and fixed it in a vice, so that the horizontal edge on which the large brass rocker 
rested was perpendicular to the surfaces of principal cleavage. Loud and sustained 
vibrations were the consequence. I repeated the experiment in the case of bismuth 
with equal success ; and after a little practice found that the precaution of cutting 
the substances in the manner just described was wholly unnecessary, and that tones 
could be obtained with facility, no matter what might be the direction in which the 
mass was cut. 
We have thus proved antimony and bismuth to be active in one position at least; 
but antimony is active both as rocker and bearer. Two irregular masses, the one 
weighing about a pound and the other five pounds, were so filed down as to present 
suitable surfaces for rocking. Heated, and placed upon a flat mass of lead, both 
masses vibrated permanently. These experiments add their evidence to that already 
adduced against the third law ; for antimony is a worse conductor than lead, and 
antimony is here the hottest metal. 
These results appear to leave the theory of Professor Forbes without any founda- 
tion, One point only remains to be considered. Professor Faraday attributes the 
superiority of lead as a bearer to its great expansibility by heat, combined with its 
deficient conducting power. Against this view Professor Forbes argues in the 
ingenious manner already described. It cannot be denied that when the supporting 
metal is a good conductor a greater quantity of heat will pass into it during contact 
mdcccliv. c 
