1867.] for multiplying and maintaining Electric Charges. 71 



I may take this opportunity of describing an application of it to illus- 

 trate a very important fundamental part of electric theory. I hope 

 soon to communicate to the Eoyal 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 com- 

 munication with a delicate electroscope or electrometer. If the lining 

 of the cistern and the inner metallic surface of the inductor be different 

 metals, an electric efl'ect is generally found to accumulate in the receiver 

 and electrometer. Thus, for instance, if the inner surface of the in- 

 ductor be dry polished zinc, and the vessel of water above be of copper, 

 the receiver acquires a continually increasing charge of negative elec- 

 tricity. There is little or no efl'ect, 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 sur- 

 face 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 ex- 

 hibited by the electrometer. When the inner surface 

 of the inductor is of bright metallic colour, either zinc 

 or copper, there seems to be little diflerence in the 

 efl'ect 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 communication M'ith 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 * indicating, 

 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 

 galvanometers, is very convenient for exhibiting these results. Its sen- 

 sibility is such that it gives a deflection of 100 scale-divisions ( of 

 an inch each) on either side of zero, as the effect of a single cell of 

 Daniell's ; the focusing, by small concave mirrors, supplied to me by Mr. 

 Becker being so good that a deflection can easily be read with accuracy 

 to a quarter of a scale-division By adopting Peltier's method of a small 

 magnetic needle attached to the electric moveable body (or " needle "), 



* See Nichol's Encyclopedia, 1860, article "Electricity, Atmospheric :" or Proceedings 

 of the Eoyal Institution, May 1860 ; lecture on Atmospheric Electricity. 



