102 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
fulcrum are 1 and 13*6, was hung a brass wire W, 8 inches long and 0‘2 inch diameter, 
by means of an insulated hook with a clamp for connexion with one plate of the 
condenser C. The wire was strained down in opposition to a small weight on the long 
arm of the steel-yard by means of the insulated screw-hook S connected with the 
contact-key K ; when the cha,rge is to be sent through the wire, this key has to be 
pressed down. To the metallic support of the lever is attached one terminal of a 
Fig. 27. 
single cell A Z, the other terminal being connected through a Thomson-galvanometer 
G to the adjustable metallic fork It. If contact between the long arm of the steel- 
yard and either the top or bottom of the fork takes place, then a current passes and 
the movement of the galvanometer indicates that the wire has either shortened or 
lengthened. When the long arm of the lever was adjusted to O'OOl inch from 
touching the top or the bottom of the fork, as the case might be, and the charge in 
the condenser was sent through the wire, contact was not made, showing that no 
shortening or lengthening to the extent of x 3 6 X 0 0 - inch occurred at the time of the 
discharge. When 8 inches of platinum wire, 0'0125 inch diameter, was experimented 
with, no instantaneous shortening of the wire took place at the moment of its 
deflagration. When 8 inches of iron wire, 0‘03 inch diameter, was experimented with, 
a downward movement of the long arm of the lever to the extent of 0'375 inch 
occurred, showing an elongation by the heating effect of the discharge of ^ ^ I- = 
0 ‘02786 inch ; the contraction of the wire in cooling brought the long arm of the lever 
to nearly, but not quite, its normal position ; the elongation indicates a temperature 
of about 300° C., but it is most probable that it was higher, so that it may be safely 
concluded that the elongation of the wire was solely due to the heat. 
We have made experiments to ascertain the amount in chemical equivalents required 
to fully charge the 42 ‘8 microfarads accumulator by connecting a voltameter in the 
circuit to one of its plates, from one terminal of the battery, the other terminal to the 
other plate. The connexion in every case was continued for two minutes, although the 
evolution of the mixed gases in the voltameter had nearly ceased in thirty seconds ; a 
very minute quantity, indeed, of gas continues to be liberated, however long the 
accumulator remains in connexion with the battery ; this we attribute to a leakage. 
