ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 
491 
observations. For the suggestion of the Leyden-jar and the plan of observation about 
to be described we are indebted to Professor Stokes, by whose advice we have often 
profited. The arrangement of the apparatus is shown in fig. 14. 
It will be seen on reference to fig. 14 that a battery of chloride of silver cells, the 
centre to earth, is used to charge up the opposite quadrants of the electrometer with 
electricity of opposite names. The number of cells is generally varied from 10 up to 60 
in order to regulate the deflection, which can also be varied by varying the distance 
between the plates P and Q of the induction apparatus. 
The needle is connected to the inside of the Leyden-jar L, the outside being 
permanently connected to earth. By pressing down the key a (which is supposed to 
represent a mercury connexion, as do also the keys b and c) the inside of the jar is 
connected with the induced plate Q ; before, however, connecting the source of elec¬ 
tricity with P, the key b is pressed down so as to connect the inside of the jar, the 
needle, and the induced plate Q to earth ; this may be designated the Q system. 
The source of electricity is now connected by means of T T 7 to the inducing plate P; 
this may be designated the P system. No charge under this arrangement is possible 
in the system Q which is to earth, consequently the needle remains undisturbed. 
The wire T 7 is now disconnected, b raised to disconnect the Q system from earth ; 
up to this point there is no deflection, but the instant that the P system is discharged 
to earth by pressing down the key c then there occurs a negative deflection; in order 
to decrease the leakage to a minimum the key a is raised so as to disconnect Q from 
the Leyden-jar. 
In order to avoid waste of time, and disturbances of the readings by possible leakage 
by waiting for the needle to come to rest, the resting point was determined by means 
of a formula from two consecutive turning points. 
The diagram fig. 15 represents the zero of the scale, the zero 17 of the readings, 
the first turning point A, the second turning point B, and the resting point R ; 
3 represents the third turning point, and 4 the fourth. 
623 
a 
42 0 4 
R| ! 
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Fiv. 15. 
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315 
B 
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R=B+c(A-B) 
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17 Q 
N'm 
c is a factor determined once for all, by causing tne needle to swing by means of 
an electric charge and then discharging ; so that the subsequent swings are due 
solely to the torsion of the bifilar suspension. Four sets of observations were made 
