222 MR. HARRIS ON SOME ELEMENTARY LAWS OF ELECTRICITY. 



as sufficient to account for them, it should be equally applicable under whatever 

 peculiar form they may present themselves. 



22. If these phenomena, then, be considered in reference to the accumulation of 

 electricity on conducting bodies, there may appear some reason to conclude, that a 

 portion of the whole force becomes, as it were, masked in respect of the electro- 

 meter. Thus, taking two terms only, the force evinced by a single quantity, by the 

 method of experiment above explained (20.), fig. 9, amounted to three grains, whilst 

 the addition of a second equal quantity produced a force of nine grains, making a 

 total of twelve grains : the mean of this would be six grains ; so that if, for the sake 

 of illustration, it is admissible to reason in this way, at least one half the attractive 

 force of which the first quantity is susceptible has been masked by the operation of 

 some peculiar influence. Now this influence may consist in an electrical change 

 induced by the redundant electricity in the superficial particles of the given substance, 

 by which they exert on the accumulation, an attractive force of a greater or less ex- 

 tent, and hence, as in the examples above cited (21.), neutralize some of the force in 

 respect of the electrometer. This is not altogether an hypothetical view, since the 

 attractive force itself is evident (27- f^i and we know of no instance of electrical 

 attraction unaccompanied by previous induction. 



23. These considerations lead us to distinguish three elements peculiar to the con- 

 ditions of electrical accumulation. 



1°. The comparative quantity actually accumulated. 

 2°. The quantity not sensible to the electrometer. 

 3°. The quantity appreciable by the electrometer. 



We may distinguish the first of these by the general term quantity, and the latter 

 by the terms controlled and free quantity, or otherwise, controlled and free action. 



24. We are here led to consider the more immediate acceptation of the terms ten- 

 sion and intensity as applied to electricity, — terms not unfrequently employed in this 

 department of science in an indefinite sense. Tension denotes the elastic force of a 

 given quantity accumulated in a given space, and is therefore directly as the density of 

 the stratum ; and this I apprehend should be really the true sense of the term tension 

 in electricity on the hypothesis that electricity is an elastic fluid. It is accordingly 

 so accepted by many profound writers in physics*. 



But the term intensity, as universally understood, must be taken in a somewhat 

 different sense to this, since it has been invariably applied to the indications of the 

 electrometer, and is immediately referable to what we have called the free action (23.), 

 that is, to the operation of either a part, or the whole of the total force in a given 

 direction up to the point of discharge : thus, for example, when a double quantity of 

 electricity is accumulated on a given extent of surface, the action in the direction of 

 the electrometer is four times as great. We must not, therefore, confound the terms 

 intensity and tension (except by an especial convention in language), since by the 



* Hauy's Natural Philosophy. 



