156 



June 20, 1839. 



JOHN W. LUBBOCK, Esq., V.P. and Treas., in the Chair. 



Sir Thomas Dyke Acland, Bart., M.P., Edwin Guest, Esq., and 

 John Hogg, Esq., M.A., were balloted for and severally elected into 

 the Society. 



The following papers were read : viz. 



1. "Inquiries concerning the Elementary Laws of Electricity. 

 Third Series. By W. Snow Harris, Esq., F.R.S. 



ITie author states, that it has been his object, in this series of in- 

 vestigations, to perfect the methods of electrical measurement, whe- 

 ther relating to the quantity of electricity, intensity, inductive 

 power, or any other element requiring an exact numerical value, and 

 by operating with large statical forces both attractive and repulsive, 

 to avoid many sources of error inseparable from the employment of 

 extremely small quantities of electricity, such as those affecting the 

 delicate balance used by Coulomb. He then describes some im- 

 provements in his hydrostatic electrometer, an instrument already 

 mentioned in his first paper, which, although not available for the 

 measurement of such minute forces as those to which the balance of 

 torsion is applicable, is still peculiarly delicate and well adapted to 

 researches in statical electricity. Its indications depending on the 

 force between two opposed planes operating on each other under 

 given conditions, are reducible to simple laws, and are hence in- 

 variable and certain ; the attractive force between the discs is not 

 subject to any oblique action, is referable to any given distance, and 

 may be estimated in terms of a known standard of weight. The 

 author next proceeds to the further consideration of the subject of 

 his former papers, viz. the elementary laws of electrical action. He 

 proves, by the following experiments, that induction invariably pre- 

 cedes, or at least accompanies attraction and repulsion. 



A circular disc of gilded wood, about six inches in diameter, is sus- 

 pended by an insulating thread of varnished silk from a delicate ba- 

 lance ; a delicate electroscope is attached to this disc, and the whole 

 is counterpoised by a weight. A similar disc insulated on a glass 

 rod, and having also an electroscope attached to it, is placed at any 

 convenient distance immediately under the former. One of the lower 

 discs being charged with either electricity and the other remaining in- 

 sulated and neutral, the electroscope of the neutral disc begins to 

 rise, whilst that of the charged disc, already in a state of divergence, 

 tends to collapse : when these respective effects ensue, the suspend- 

 ed disc descends the charged disc. Two inductive actions are in- 

 dicated in this experiment, the one the author considers to be a di- 

 rect induction, the other a reflected induction. 



If the two discs are both charged with opposite electricities, on 

 opposing them as before, the electroscopes begin to fall back, at 



