founded on Induction and Convection. 69 



dry pile (zinc, copper, paper), applied with one pole to one of the 

 inductors, and the other for a moment to the connecting springs 

 and the other inductor, may be used to determine, or to suddenly 

 reverse, the character (vitreous or resinous) of the electrification 

 of the insulated inductor. The only instrument yet made is a very 

 small one (with carrier-wheel 2 inches in diameter), constructed 

 for the Atlantic-Telegraph application ; but its action has been 

 so startlingly successful that good effect may be expected from 

 larger machines on the same plan. 



When this instrument is used to replenish the charge of the 

 inductor in the constant electric machine, described above, one 

 of its own inductors is connected with the earth, and the other with 

 the inductor to be replenished. When accurate constancy is de- 

 sired, a gauge-electroscope is applied to break and make contact 

 between the connector-springs of the replenisher when the po- 

 tential to be maintained rises above or falls below a certain limit. 



Several useful applications of the replenisher for scientific 

 observation were shown by the author at the recent Meeting of the 

 British Association (Dundee), — among others, to keep up the 

 charge in the Leyden jar for the divided-ring mirror-electrometer, 

 especially when this instrument is used for recording atmo- 

 spheric electricity. A small replenishes attached to the instru- 

 ment within the jar, is worked by a little milled head on the out- 

 side, a few turns of which will suffice to replenish the loss of 

 twenty-four hours. 



Postscript, Nov. 23, 1867. 



As has been stated, this machine was planned originally 

 for recording the signals of the Atlantic Cable. The small " re- 

 plenisher " represented in the diagrams has proved perfectly suit- 

 able for this purpose. The first experiments on the method for 

 recording signals which I recently patented were made more 

 than a year ago by aid of an ordinary plate-glass machine worked 

 by hand. This day the small " replenisher " has been connected 

 with the wheelwork drawing the Morse paper on which signals 

 are recorded, and, with only the ordinary driving-weight as 

 moving power, has proved quite successful. 



The scientific applications indicated when the communication 

 was made to the British Association have been tested within the 

 last few weeks, and especially today, with the assistance of Pro- 

 fessor Tait. The small replenisher is now made as part of each 

 quadrant electrometer. It is permanently placed in the interior 

 of the glass Leyden jar ; and a few turns by the finger applied to 

 a milled head on the outside of the lid are found sufficient to reple- 

 nish the loss of twenty-four hours. A small instrument has also 



