ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 
229 
say to the right, for the make-contact or inverse current ; the contact was then 
broken and the swing, say to the left, was that for break-contact or direct current. 
It is almost needless to state that the primary current was suitably reduced by 
inserting resistances in the circuit, and that of the secondary by the use of suitable 
shunts to prevent injury to the Thomson galvanometer. 
Having thus ascertained the direction of swing for direct or inverse currents, the 
condenser was connected up, the short-circuit plug having been previously inserted 
between the terminals of the galvanometer so as to prevent any disturbance of it on 
making contact ; as soon as the condenser had acquired a sufficiently high potential 
the short-circuit plug was removed. If the battery were left on there was frequently 
a slight inverse (make-contact) current indicated by the swing of the galvanometer. 
If the battery was now (after the insertion of the short-circuit plug) disconnected, 
there was a continuous direct current observed as the charge of the condenser ran 
gradually down so soon as the short-circuit plug was removed. The first of the two 
cases was equivalent to an infinite number of make-contacts, the second to an infinite 
number of break-contacts. Many observations were made with coil No. 819, which 
we had taken to pieces several times during the course of our trials on account 
of suspected leakage from the primary to the secondary wire. It was ultimately 
entirely remade in February, 1878, and the secondary wire coiled on a separate 
ebonite cylinder to ensure efficient insulation, which was accomplished. 
Coil 819 when altered was thus composed. 
Approximate 
internal 
diameter. 
External 
diameter. 
Length of 
■wire. 
Diameter of 
wire. 
Resistance. 
Turns. 
inch. 
inch. 
inch. 
ohms. 
0-6 
2-2 
1700 yards 
0-014 
0-304 
12920 primary. 
3-2 
4-6 
14 miles 
0-0033 
42000 
26289 secondary. 
In every case where the strata are to the eye or rotating mirror perfectly steady, 
slight deflections of the needle are seen ; these generally indicate a resultant direct 
current (break-contact), and in the fewer number of cases an inverse current 
indicating, in the first case, a sudden decrease and slow increase of current through 
the tube. These deflections, though very manifest, do not amount to more than 
about three or four divisions of the galvanometer scale, a deflection which indicates 
a current of only 0'00000000023 W. At the advent or retreat of a stratum at 
the positive pole there is frequently produced a deviation of 300 divisions, indicating 
a current of 0 '00000001 812 W; before a stratum leaves the positive terminal or dies 
out on it, there is usually a tremulous motion of that stratum visible to the eye and 
indicated by rapid pulsations of the galvanometer. 
On the suggestion of Professor Clerk Maxwell we have recently introduced 
the telephone into the primary current, as shown in fig. 70, and also in the secondary 
current of coil 819. 
