692 PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 
K, K and D, D, thick copper supports for the zinc plates, the zincs of R, R being 
firmly clamped to K, K, and those of S, S to D, D. 
E, E, a thick conductor connecting the coppers of series R, R together. 
F, F, a similar conductor connecting the coppers of S, S. 
Fig. 7. 
H, H, a bundle of wires connecting the coppers of S, S with the zincs of R, R. 
M, M, a wooden partition separating the battery-room from the experimenting-room. 
L and M are two bundles of wire which pass through holes in the partition and 
connect the commutator G respectively with the coppers of series R, R, and the 
zincs of series S, S. The bundles of wires O and P complete the circuit through XY, 
the conductor to be tested. 
The dotted spaces round the porous cells represent shelves for holding crystals oi 
sulphate of copper. 
65. After about an hour and a half, the thermometer at the middle of the conductor 
indicated 170° Fahr. (76°7 Cent.) ; and one of the brass bridges of the commutator was 
then lifted so as to break the circuit. Immediately the liquid mounted rapidly in 
each of the three glass tubes of the air-thermometers, and it was prevented from 
rising above a certain point in the middle one by completing the circuit again. The 
column of liquid was kept as steady as possible at this point in the middle air-ther- 
mometer by a person observing it, and making and breaking the circuit by means of 
the brass bridge, while two other persons noted the indications of the two lateral air- 
thermometers, The current was reversed every three or four minutes, and the liquid 
in the middle air-thermometer brought back to the same point, and kept as nearly 
as possible to it. The imperfection of the regulating system was such as to make it 
very difficult to prevent great oscillations in the thermometers, but the instantaneous 
manner in which their indication followed the operations of the break made it cer- 
tain that the plan would be perfectly successful when a continuously acting regulator 
should be introduced. 
