106 Vibrations of Trevelyan’s bars by the Galvanic Current. 
continued at pleasure without the trouble of reheating the bars 
for each trial. After various fruitless efforts I obtamed a most 
beautiful result by using the heating power of a galvanic current. 
Fig. 1 shews the mode of performing the experiment with the 
of brass, and weighing from one to two pounds, and after being 
sufficiently heated, are placed upon a cold block of lead as seen 
in fig. 2. The two bars 2. 
may be placed upon the 
same block though the vi- 
brations are apt to interfere 
when two are used. 
any kind of metal,—brass or 
copper or iron, however, seeming to be most convenient. One 
or both of the bars may be placed at once without reference to 
temperature upon the stand, as in fig. 1, the bars resting upon me- 
tallic rails, E, F', which latter are made to communicate each with 
the poles of a galvanic battery of some considerable heating 
power. ‘T'wo pairs of Daniell’s, of Smee’s, or of Grove’s battery 
of large size are sufficient. The battery I employ consists of two 
airs of Grove’s with platinum plates four inches square. The 
vibration will proceed with great rapidity as long as the galvanic 
current is sustained. 
In fig. 2, one pole of the battery is connected with the metallic 
block and the other pole with mercury in a little cavity in the 
centre of the vibrating bar. The experiment succeeds much better 
with the rails, as in fig. 1, and quite a number of bars may be 
kept in motion by increasing the number of rails and passing the 
current from one to the other through the bars resting a. 
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