THE CONTACT OF BODIES HAVING DIFFERENT TEMPERATURES. 
7 
The experiments were repeated with fumy quartz, and the same result was ob- 
tained. 
2. Fluor-spar. — A smaller brass rocker than that last used was found to answer 
best with this crystal. The dimensions corresponding to AC, AB, fig. 1, were 3*8 
inches and 125 inch respectively ; while the depth was the same, or nearly so. This 
rocker having been placed upon the natural edge of the crystalline cube, a clear and 
melodious note was instantly produced. Forcible vibrations were also obtained with 
the larger rocker, but not so clear a tone. 
The angle of the cube was cloven off so as to expose the edge of the octahedron ; 
on this edge also vibrations were obtained. 
Fortification Agate. — Distinct vibrations and tones were obtained with the large 
brass rocker. I found it sometimes convenient to increase the time of oscillation by 
laying a thin brass bar with small knobs at the ends, across the rocker — a mode of 
experiment due, I believe, to Mr. Trevelyan. With this precaution, in the case 
before us, the rocker continued swinging for nearly half an hour, and when it ceased 
it was under the temperature of boiling water. 
Rock-salt. — The rocker used in the foregoing experiment was laid aside and a 
piece of rock-salt was prepared for trial. The mass was cloven so as to exhibit the 
surfaces of the primitive cube ; and was so placed that the straight line formed by 
the intersection of two of the surfaces of the cube was horizontal. Previous to 
heating the rocker, I laid it, according to practice, upon the mass, merely to ascertain 
whether the arrangement was likely to answer. To my astonishment a deep musical 
sound commenced immediately. The temperature of the rocker was at this time far 
below that of boiling water, and when it had ended its song it was scarcely above a 
blood heat. 
The heated rocker was laid upon a large boulder-shaped mass of the salt ; it com- 
menced to sing immediately. I scarcely know a substance, metallic or non-metallic, 
with which vibrations can be obtained with greater ease and certainty than with 
this mineral. To the remarkable properties which the researches of Melloni have 
shown to belong to rock-salt a new one may now be added. 
Avanturine. — I was tempted to try this mineral from having met a piece of it pos- 
sessing a clean sharp edge. The large brass rocker placed hot upon this edge gave 
a decided tone. 
Sulphate of Potash.-— Care is required with this artificial crystal, as it readily flies 
to pieces on the sudden communication of heat. With proper precautions, feeble, 
but well-established vibrations, were obtained. 
Onyx. — A distinct tone. 
Tourmaline. — After many trials I obtained a continuous vibration and low tone. 
Fossil Wood. — Two different specimens were examined and distinct tones obtained 
with both of them. 
Banded Agate. — Strong and continuous vibrations, when the rocker was very hot. 
Chalcedony . — Loud and long-continued knockings on a knob of this mineral. 
