1868.] Mr. R. L. J.Ellery on a Pendulum-Eledrograph, 463 



charge-measuring disk is now approached to the pendulum-disk until a suf- 

 ficient deflection is caused to alter the scale-reading (say, 1 0') from the zero, 

 and the indication of the slide-tube and screw noted as charge-reading. The 

 electrodes are now disconnected from the earth and connected with the 

 12-cell battery, one with one pole and one with the other, and the deflection 

 then read off ; the poles are then reversed and a second reading obtained. 

 The charge-reading is now obtained again, as well as the zero-reading. 

 The following actual observations will further elucidate this : — 



Scale-reading. Screw-reading. 



Zero 96-5 



Charge 940 



Battery P 101*6 



Battery N 90-4 



Charge 940 



Zero 96-2 



The reading for battery in first positions diff'ers from zero by -f5*l divi- 

 sions, and in the second by —5*8 divisions. A deflection of .5*45 divisions 

 is therefore equal to twelve Daniell's cells when the charge-reading is 

 940. The charge is now reduced and the same process is gone through. 

 This is repeated for eight or ten degrees of charge ; and by this means we 

 obtain a set of readings of the amount of deflection caused by a 12-cell 

 battery for various states of the charge, as well as arbitrary measures of the 

 charge by the screw- and slide-tube. 



One set of observations gave the following results : — 



When the reading of the 

 charge-measurer (with the 

 disks near enough to pro- 

 duce a deflection of 10') is 



Twelve cells Daniell's 

 battery causes a deflec- 

 tion of pendulum of 



1*00 0*06 scale-divisions. 



2-00 

 3*00 

 4*00 

 5*00 

 6*00 

 7-00 

 8*00 

 9*00 



076 

 1*39 

 1*90 

 2*35 

 2*80 

 3-32 

 3-96 

 4*80 



10-00 5*89 



11*00 7-30 



12*00 9-09 



The distances between the disks when the charge-measurer reads 1*00 

 and 12*00 were 1*16 inch and 3 inches respectively. From this a Table is 

 computed, in which the value of the scale-reading and of the ordinates to 



