for multiplying and maintaining Electric Charges. 395 



recently brought before the Royal Society by Mr. C. "W. Siemens 

 and Professor Wheatstone, and mathematically investigated by 

 Professor Clerk Maxwell. Indeed it was from the fundamental 

 principle of this electromagnetic system that the reciprocal part 

 of the electrostatic arrangement occurred to me recently. The 

 particular form of self-acting electrophorus condenser now de- 

 scribed, I first constructed many years ago. I may take this op- 

 portunity of describing an application of it to illustrate a very 

 important fundamental part of electric theory. I hope soon to 

 communicate to the Hoyal Society a description of some other 

 experiments which I made seven years ago on the same subject, 

 and which I hope now to be able to prosecute further. 



Using only a single inductor and a single receiver, as shown in 

 fig. 1, let the inductor be put in metallic communication with a 

 metal vessel or cistern whence the water flows ; and let the receiver 

 be put in communication with a delicate electroscope or electro- 

 meter. If the lining of the cistern and the inner metallic surface 

 of the inductor be dhTerent metals, an electric effect is generally 

 found to accumulate in the receiver and electrometer. Thus, for 

 instance, if the inner surface of the iuductor be dry polished zinc, 

 and the vessel of water above be of copper, the receiver acquires a 

 continually increasiug charge of negative electricity. There is 

 little or no effect, either positive or negative, if the inductor present 

 a surface of polished copper to the drops where they break from 

 the continuous water above : but if the copper surface be oxidized 

 by the heat of a lamp, until, instead of a bright metallic surface 

 of copper, it presents a slate-coloured surface of oxide of copper 

 to the drops, these become positively electrified, as is proved by a 

 continually increasing positive charge exhibited 

 by the electrometer. When the inner surface 

 of the inductor is of bright metallic colour, 

 either zinc or copper, there seems to be little 

 difference in the effect whether it be wet with 

 water or quite dry ; also I have not found a 

 considerable difference produced by lining the 

 inner surface of the inductor with moist or 

 dry paper. Copper filings falling from a copper 

 funnel and breaking away from contact in the 

 middle of a zinc inductor, in metallic commu- 

 nication with a copper funnel, as shown in fig. 

 4, produces a rapidly increasing negative charge 

 in a small insulated can catching them below. 



The quadrant divided-ring electrometer * in- 

 dicating, by the image of a lamp on a scale, 

 angular motions of a small concave mirror (-i- 

 of a grain in weight) such as I use in galvano- 

 meters, is very convenient for exhibiting these 



Pig. 4. 



* See Nichol's Encyclopaedia, 1860, article "Electricity, Atmospheric ;" or Pro- 

 ceedings of the Koyal Institution, May 1860, lecture on Atmospheric Electricity. 



2 D 2 



