322 Mr. F. C. Webb on one of Ohm's Laws 



city is diffused in the galvanic circuit, and imagine this circuit 

 touched at any one place by a non-conducting body*, and desig- 

 nate by u l the electric force at this place before contact, by u that 

 after contact, the change produced in the force in this place is 

 u l — it; consequently the change of the whole quantity of elec- 

 tricity in the circuit is (u { — u)r. If, now, we suppose that the 

 electricity in the touched body is diffused over the space R, and 

 is at all places of equal strength, and at the same time that at the 

 place of contact itself the circuit and the body possess the same 

 electric force, viz. u, it is evident wR will be the quantity of elec- 

 tricity imparted to the body, and 



(u l — u)r=uR, 

 whence we obtain 



u-,r 



u= — ^^r* 



r + R 



The intensity of the electricity received by the body will there- 

 fore be the more nearly equal to that which the circuit possessed 

 at the place of contact before being touched the smaller R is 

 with respect to r ; it will amount to the half when R = r, and 

 become weaker as R becomes greater in comparison with r." 



This problem, as stated by Ohm, if taken according to the 

 strict reading of the wording, is not correct, and requires a 

 further proviso, as will easily be seen. 



Ohm has treated all bodies as having an inductive capacity 

 simply proportional to their surface, in which case the " density J> 



(or - — -, — -) would always be proportional to the "tension" 



"potential. 33 Consequently one term would serve for both these 

 properties of electricity ; and accordingly we find the term " elec- 

 troscopic force," employed by Ohm, standing indiscriminately for 

 both tension and density. 



Thus we find, in defining what Ohm calls " tension " (i. e. elec- 

 tromotive force of modern language), the following quotation, 

 showing the word " electroscopic force " employed as tension or 

 potential of our present phraseology : — 



" The mode in which electricity makes its appearance at the 

 place of contact of two different bodies, or the electrical tension 

 of these bodies, I have thus expressed : when dissimilar bodies 

 touch one another, they constantly maintain at the point of con- 

 tact the same difference between their electroscopic forces" 



And again : — 



" Different bodies which touch each other constantly preserve 

 at the place of contact the same difference between their electro- 

 scopic forces, by virtue of a contrariety proceeding from their 

 * This should evidently be " an insulated conducting body." 



or 



