Mr. W. S. Harris on the Elementary Laws of Electricity. 321 



provements in his hydrostatic electrometer, an instrument already- 

 mentioned in his first pajier, 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 jiext 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 aie 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 

 which moment the discs appear to attract each other. But if the 

 discs are both charged with the same kind of electricity, the diver- 

 gence of the electroscopes increases, and at this instant the suspended 

 disc recedes from that which is fixed, being apparently repelled 

 by it. 



The author proceeds to examine strictly the nature of this in- 

 ductive influence, and adduces experiments to render probable that 

 it is in some way dependent on the presence of an exquisitely subtile 

 form of matter which may become disturbed in bodies, and assumes 

 new states or conditions of distribution. 



Very numerous experiments are detailed, showing the influence of 

 changes of different intensity, of changes in the dimensions and di- 

 stances of the opposed discs, of interposed bodies of different forms, 

 &c. on the phenomena of induction. The auJthor concludes by giving 

 the following formulae as the results of his investigations regarding 

 the elementary laws of elecirical induction and attraction. In these 

 expressions Q = quantity of charge, T = the direct induction, 

 q = the quantity of electricity displaced, t = its intensity, T =. the 

 reflected induction, ^' = the disturbed quantity, ^' := its intensity, 

 y" = the total quantity in the opposed charged surface, A = the 



FUl. Mag. S. 3. Vol. 15. No, ^Q>. Oct. 1839. Y 



