250 



measures very small and not of much value, the penetration of the 

 succeeding measures may be taken as '014, '025, '045, that is '007, 

 0125, '0225 upon each of the opposed exploding points, taking the 

 surfaces of the exploding balls as curvilinear coatings to the inter- 

 vening air. 



If any considerable spreading of the charge upon the uncoated 

 glass should arise, that, as remarked by Cavendish, would be equiva- 

 lent to an increase of the coating, and hence the tension due to a 

 given quantity of charge would be less. The effect would be greater 

 on the first measured quantity than on succeeding quantities ; hence 

 for explosion at a first distance, an additional two or three measures 

 might be required, which, as the spread upon the glass became 

 satisfied, might not be requisite in the same proportion upon suc- 

 ceeding measured distances, in which case discharge would ensue 

 with a less number of measures than calculation determines according 

 to Lane's law, making it appear as if, according to Nicholson, " the 

 intensity ran before the quantity." 



Both Franklin and Nicholson have taken a sound practical and 

 theoretical view of electrical accumulation on coated glass, which the 

 author conceives to depend on a play of opposite electrical forces, 

 either directly through the glass intermediate between the coatings, 

 or through the medium of an external circuit, or both. He con- 

 siders the terms "free" and " compensated," or "latent" electri- 

 city, perfectly admissible when correctly applied and limited by sound 

 definition. All the accumulated charge, up to the exploding point, 

 is evidently not sensible to the electrometer, and he thinks it con- 

 venient to distinguish between that portion of the charge of which 

 the electrometer directly says nothing, and that portion to which its 

 indications are more immediately referable, more especially as these 

 two, or conjugate portions, have important relations to each other. 

 Thus a double measured charge has twice the amount of free charge ; 

 and the free charge, as estimated by attractive force, is as the square 

 of the accumulation. When the free charge explodes, the whole 

 accumulation, or nearly all, goes with it, at least in common cases of 

 metallic coated glass, and according to Nicholson carries it through 

 distances proportionate to the charge itself : the terms " free " and 

 "latent " electricity, or, as the French have it, " electricitedissimulee," 

 may not be exact or admissible, if meant to imply a difference in kind 



