214 TVIR. HARRIS ON SOME ELEMENTARY LAWS OF ELECTRICITY. 



resorted to in the prosecution of physical inquiries. Accordingly, I am led to avail 

 myself of it, but without extending it beyond the simple principle above mentioned. 

 The properties of this subtile matter, whether of an elementary or compound charac- 

 ter, if such should hereafter be more fully proved to exist, I leave only to be deter- 

 mined by adequate induction from observed phenomena. 



4. Assuming, then, as an elementary principle, not upon the whole unwarranted by 

 facts, the existence of a subtile material agent essentially involved in the constitution 

 of ordinary matter, and known to us only through the medium of its effects, we may 

 distinguish its presence under two different forms of what may be termed electrical 

 excitation ; that is to say, a state of excitation produced by a different relative state 

 of the electricity possessed by a body to that which is more or less common to all 

 bodies, in which case the quantity remains unchanged ; and a state of excitation de- 

 rived from an actual addition, or subtraction, of the electricity of a given substance, 

 or of any component part of its electricity, in which case the quantity may be said 

 to vary. 



5. The latter of these states has been termed excitation by communication ; and the 

 former, when produced by the influence of this last, operating at a distance, excitation 

 by induction. 



6. A body, when excited according to either of these forms of excitation, displays 

 apparently an attractive force, so that other bodies, when all impediments to motion 

 are removed, tend toward it, and the accumulated electricity seeks to regain its pre- 

 viously existing state : a peculiar action is in this case found to obtain, either in the 

 excited substance itself, or otherwise between it and the surrounding masses. Such 

 may be considered, on the above hypothesis, the great characteristics of ordinary 

 electrical action, those which were the first observed, and which, with their attendant 

 phenomena, demand the most rigorous scrutiny. 



7. In order to facilitate the progress of inquiries concerning the elementary laws of 

 electrical action, I have been led to construct one or two new instruments, as also to 

 resort to other electrical arrangements, which it is essential to notice. Fig. 1. A. 

 (Plate II.) represents an electroscope which acts on the principle of divergence : a 

 small elliptical ring of metal, a, is attached obliquely to a small brass rod, a b, by the 

 intervention of a short tube of brass at a ; the rod a h terminates in a brass ball, &, and 

 is insulated through the substance of the wood ball n : two arms of brass, rr\ are fixed 

 vertically in opposite directions, on the extremities of the long diameter of the ring, 

 and terminate in small balls ; and in the direction of the shorter diameter, within the 

 ring, there is a delicate axis set on extremely fine points : this axis carries, by means 

 of short vertical pins, two light reeds of straw, terminating in balls of pith, and con- 

 stituting a long index A, corresponding in length to the fixed arms above mentioned. 

 The index thus circumstanced is susceptible of an extremely minute force ; its ten- 

 dency to a vertical position is regulated by small sliders of straw, moveable with suf- 

 ficient friction on either side of the axis. To mark the angular position of the index 



