KoklvauschontkeElectroscopicPropertiesoftheVoltaicCircuit. 323 



pher's speculations place before us. The comparative want of re- 

 cognition which the other portions of the theory have experienced, 

 is to be chiefly referred to the difficulty of procuring instruments 

 sufficiently delicate to test them experimentally. By the inven- 

 tion and skilful application of suitable instruments, M. Kohlrausch 

 has been able to travel side by side with the speculations of Ohm, 

 and to convert them one after another into experimental facts. 



The fundamental portions of Ohm's theory may be briefly 

 sketched as follows : — Let the ring, Plate IX. fig. 1, represent a 

 homogeneous conductor, and let a source of electricity be supposed 

 to exist at A. To fix the ideas, let us suppose an electric machine 

 placed there. The electricity from the machine will diffuse itself 

 over both sides of the ring ; the positive passing towards a, and 

 the negative towards b, both fluids uniting at c. Now if the 

 electricity be so distributed over the ring that a heaping up of 

 the fluid nowhere occurs, then it follows that equal quantities 

 of electricity pass through all cross sections of the ring in the 

 same space of time. If it be assumed that the passage of the 

 fluid from one cross section to another is solely due to the differ- 

 ence of the electric tension at both these points ; and further, 

 that the quantity which passes is proportional to this difference 

 of tension, the consequence is, that the positive fluid proceeding 

 from A right to c, and the negative fluid proceeding from A left 

 to c, must decrease in tension the further they recede from A. 



The tension of the electricity at every point in the circuit may 

 be represented by a diagram. Let the above ring be supposed 

 to be stretched out into a straight line A A', fig. 2 ; let the ordi- 

 nate AB represent the tension of the positive electricity, and 

 A'B' the tension of the negative electricity at the point of excita- 

 tion, then the ring being homogeneous and of the same diameter 

 throughout, the straight line BB' will express the tension for all 

 points of the circuit. 



From these considerations, the law of Ohm expressed by the 

 celebrated formula 



s- E 



where S represents the strength of the current, E the electro- 

 motive force of the battery, and R the resistance, naturally fol- 

 lows. If the electromotive force AB + A'B' remain constant, 

 then the greater the length of AA' the less steep will be the in- 

 clination of the line BB' ; that is to say, the less will be the dif- 

 ference of tension in two contiguous cross sections. But by the 

 hypothesis, this difference is proportional to the quantity of fluid 

 which passes from one cross section to the other; and hence it 

 follows, that the greater the length of the circuit, the less will 



y 2 



