153 
mation, and the suggestiveness of Mr Gore’s experiment on the 
rolling-ball, will be judged of from the fact, that in 1833, or earlier, 
I had an apparatus made, consisting of a bar resembling Mr Treve- 
lyan’s, but longitudinally divided by a non-conducting partition, 
while the two conducting sides were furnished with mercury cups for 
connecting them with the poles of a battery, the circuit being com- 
pleted through the metallic base. The instrument exists, or existed 
a few years ago, though I am at present unable to find it. As well 
as I recollect, it was tried with an old-fashioned Cruickshank’s bat- 
tery of fifty pairs, without success. Indeed, I now find that, even 
with modern appliances, the experiment does not succeed when the 
circuit is only closed whilst both points of bearing of the rocker 
touch the mass or support. 
“ 20th December 1858.” 
“ Since the date of the preceding notice (which was prepared for 
being laid on the table of the Royal Society at their meeting on the 
20th ult.), I have continued and extended these experiments. As 
they are still in progress, I will content myself with mentioning two 
results as worthy of notice. I have obtained very active vibrations 
of carbon (such as is used in one of the elements of Bunsen’s bat- 
tery) resting upon brass, and also when it rests upon two pieces of 
carbon connected with the terminals of a battery. For this purpose, 
a battery having a certain amount of intensity is requisite, in order 
to overcome the resistance of carbon as a conductor, but the vibra- 
tions are most energetic. The extremely small expansion which 
takes place in carbon by heat is another argument against that view 
of the Trevelyan experiment. The other experiment to which I 
refer is, that bismuth (and perhaps other metals) are not merely in- 
active as vibrators with any electric power which I have used, but 
the passage of electricity through them appears to have a quelling 
power which brings the rocker to instantaneous rest ; yet bis- 
muth permits a far freer passage of electricity than carbon : in one 
experiment I found that sixteen times as much was conducted. 
Something analogous was formerly observed by me in connection 
with heat applied to bismuth. I am now attempting to investigate 
the subject farther by experiment. 
“ 3d January 1859.” 
