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i _ Vibrations of Trevelyan’s bars by the Galvanic Current. 107 
j 
The rails are best made of brass wire ora strip of sheet brass, 
though other metals will answer, the harder metals which do not 
oxydate readily, however, being preferred. A soft metal like lead 
is not so favorable to the vibrations in this experiment, although 
in Trevelyan’s experiment lead seems to be almost the only 
metal that will answer to support the bar which is usually made 
of brass. 
Prof. Graham and other authors have attributed the vibration 
of 'T'revelyan’s bars to the repulsion between heated bodies, and 
others have classed the phenomenon with the spheroidal state of 
heated bodies. I do not consider that any repulsive action is 
manifested or necessary in either of these cases, nor 
any instance in which a repulsion has been proved between heat- 
ed bodies. It is obvious some other solution is required for this 
curious phenomenon, and it appears to me that the motion is due 
to an expansion of the metallic block at the point of contact, and 
upon this supposition, it appears plainly why a block of lead is 
required. That is, a metal of low conducting power and high 
expansibility is necessary, and lead answers these conditions best. 
na future communication I will anlayze this matter and explain 
more fully. 
The size of the bars may be very much increased when the 
galvanic current is employed, and some curious motions are ob- 
served when long and large cylinders of metal are used. If they 
are not exactly balanced, which is almost always the case, they 
commence a slow rolling back and forth until finally they roll 
entirely over, and if the rails were made very long they would 
go on over the whole length. An inclination of the rails is re- 
quired in this case, but it may be so slight as not to be percepti- 
ble to the eye. 
+ 
3. 
et J 
If along rod of some weight be placed across one of the bars, 
a8 shown in fig. 3, the vibrations will become longer, and by way 
of amusement, I have illustrated this with a galvanic see saw as 
it may be termed. 
