1854.] OF THE ROYAL INSTITUTION. 359 
cause, the effect must be a maximum when the block is the best 
conductor possible. But Professor Forbes, in this argument, seems 
to have used the term expansion in two different senses. The ex- 
pansion which produces the vibration is the sudden upheaval of the 
point where the hot rocker comes in contact with the cold mass un- 
derneath ; but the expansion due to good conduction would be an 
expansion of the general mass. Imagine the conductive power of 
the block to be infinite, that is to say, that the heat imparted by the 
rocker is instantly diffused equally throughout the block; then, 
though the general expansion might be very great, the local expan- 
sion at the point of contact would be wanting, and no vibrations 
would be possible. The inevitable consequence of good conduction 
is, to cause a sudden abstraction of the heat from the point of contact 
of the rocker with the substance underneath, and this the Lecturer 
conceived to be the precise reason why Professor Forbes had failed 
to obtain vibrations when the cold metal was a good conductor. He 
made use of blocks, and the abstraction of heat from the place of 
contact by the cireumjacent mass of metal, was so sudden as to ex- 
tinguish the local elevation on which the vibrations depend. In the 
experiments described by the Lecturer, this abstraction was to a 
great extent avoided, by reducing the metallic masses to thin lamin, 
and thus the very experiments adduced by Professor Forbes against 
the theory supported by Professor Faraday, appear, when duly 
considered, to be converted into strong corroborative proofs of the 
correctness of the views of the philosopher last mentioned. 
f.T] 
WEEKLY EVENING MEETING, 
Friday, February 3. 
Right Hon. Baron Parke, Vice-President, in the Chair. 
W. R. Grove, Ese., Q.C., F.R.S. 
On the Transmission of Electricity by Flame and Gases. 
In the year 1730, Mr. Stephen Grey, a pensioner of the Charter 
House, was led by pursuing a series of ingenious experiments, to the 
important discovery that bodies might be divided into two classes, 
conductors and non-conductors of Electricity. Subsequent dis- 
coveries led to the knowledge that different bodies conduct Elec- 
tricity, not only very differently as to degree, but also differently as 
to mode, and as to the changes which the bodies themselves ex- 
perience while conducting electricity. We thence get conduction 
without apparent change, as by the metals,—conduction dependent 
upon chemical change, as by Electrolytes; and then again in effects 
of transmission not usually included under the term conduction, we 
