258 On Electricity produced by different Metals. [June 15^ 



XXVI. ^'On Volta^s Experiment of the Electricity produced by tlie 

 contact and separation of different Metals/^ By Warren 

 De La Rue, M.A., D.C.L., F.H.S., and Hugo W. Muller, 

 Ph.D., F.R.S. Received June 7, 1876. 



A short time since Prof. Tyndall asked one of us to lend him our 

 Thomson-Becker quadrant electrometer for a lecture illustration of the 

 electricity developed by metallic contact ; as the bifilar electrometer in 

 question had been purposely rendered much less sensitive than usual by 

 the wide separation of the suspension-threads, it was thought advisable 

 to test the instrument before sending it. This was done with a disk of 

 copper and a plate of zinc, each fastened to a stick of sealing-wax ; the 

 action even with this rough appliance was so great that it seemed desirable 

 to pursue the experiment further. 



With this object we had constructed a simple piece of mechanism by 

 Messrs. Elliott Brothers, which enables us to briug together and to 

 separate two disks, one of copper and the other of zinc, each 6 inches in 

 diameter, 400 times in a minute, and after each separation to make the 

 zinc plate touch a spring attached to an insulated conductor ; moreover, 

 by means of cams, to make earth-connexion with either disk, or with both, 

 previous to their being brought again into contact. 



20 cells of a rod of chloride-of-silver battery charged up on May 27 

 (part of the 8040 cells now in work) and in perfect action were connected 

 with the quadrant electrometer, so that the silver pole was in metallic con- 

 tact with the quadrants to be charged, while the zinc pole and the other 

 two quadrants were connected to earth. The deflection (say to the left), 

 three times repeated, was each time 95 divisions of the scale. 



When the contact-apparatus was now substituted for the battery, and 

 the insulated conductor of the zinc disk was connected with the same 

 quadrant of the electrometer with which the silver pole of the battery had 

 been connected, and the apparatus worked steadily so as to make 320 makes 

 and breaks of contact in a minute, then to make earth-connexion with 

 the copper disk after each separation of the plates and during the time 

 that the zinc was in metallic connexion with the electrometer, the deviation 

 was to the left as before, and amounted to 



150 divisions of the scale. 



150 



145 



145 



140 



150 



Mean .... 146-7 „ 



