relating to an Insulated Circuit* 323 



nature, which we are accustomed to designate by the expression 

 electric tension, or difference of bodies" (z. e. electromotive force). 



And with regard to its employment in the sense of the term 

 density, we have only to look at Ohm's definition of quantity : — 



" We shall in future term the sum of the electroscopic actions 

 referred to the magnitude of the elements — by which, therefore, 

 we have to understand the force multiplied by the magnitude of 

 the space over which it is diffused in the case where the same force 

 prevails at all places in this space — the quantity of electricity, 

 without intending to determine anything thereby with respect to 

 the material nature of electricity." 



Here, therefore, evidently since space (or surface) multiplied by 

 the " electroscopic action or force" equals the quantity of electri- 

 city, it is evident that - — -r — -equals electroscopic action or force, 



or, in fact, electroscopic action or force stands here for density. 



In the quotation stating the problem itself, it will be seen, by 

 the meaning of the words " and at the same time that at the 

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

 electric force, viz. u" that here " electric force" means tension 

 or potential; and in the following words, "it is evident uR will 

 be the quantity of electricity imparted to the body," it will be 

 seen that u there stands for density. 



It will easily be perceived also that if the body R had a greater 

 inductive capacity in proportion to its surface than had r, then, 

 although after contact the tension or potential of the body R 

 would become the same as that of the conductor r at the point 

 of contact, yet the density would be much greater on the body 

 R than on the conductor at the point of contact. These two 

 elements could not therefore both be represented by the single 

 symbol u. 



If we obtain, however, conductors for forming the circuit and 

 the body R which shall have inductive capacities exactly propor- 

 tional to their surfaces, each equal portion of these surfaces 

 having an equal inductive capacity, this objection to the problem 

 as stated by Ohm disappears ; for, as the density will at every 

 point be exactly proportional to the tension at that point, the 

 quantity will be proportional to the tension or "electroscopic 

 force " multiplied by the surface over which such tension is dis- 

 tributed. 



Long lengths of submarine cables of the same pattern through- 

 out fulfil these conditions; and further, as their surfaces are 

 proportional to their lengths, we need only take their lengths as 

 the values of r and R. 



During the manufacture of the Persian-Gulf Cable at Mr. 

 Henley's Works, North Woolwich, when in charge of the testing- 



Y2 



