482 OHM ON THE GALVANIC CIRCUIT. 



But how must, in each separate case, a given galvanic appa- 

 ratus be arranged so as to produce the greatest effect ? Let us 

 suppose, in solving this problem, that we possess a certain mag- 

 nitude of surface ; for instance, of copper and zinc, from which 

 we can form, according to pleasure, a single large pair of plates, 

 or any number of smaller pau's, but in the same proportion, 

 and, moreover, that the liquid between the two metals is constant- 

 ly the same, and of the same length, which latter supposition 

 means nothing more than that the two metals between which 

 the liquid is confined retain, under all circumstances, the same 

 distance from each other. 



Let A be the reduced length of the body upon which the 

 electric current is to act, L the reduced length of the apparatus 

 when formed into a simple circuit, and A its tension; then, 

 when it is altered into a voltaic combination of x elements, its 

 present tension will be x A, and the reduced length of each of 

 its present elements x L, accordingly the reduced length of all 

 the X elements a?- L, consequently the magnitude of the action of 

 the voltaic combination of a? elements is 



X K 

 07'^ L + A' 



This expression acquires its greatest value — ' M-hen 



A 



a? = v' T^- We hence see that the apparatus in form of a 

 L 



simple circuit is most advantageous, so long as A is not greater 

 than L ; on the contrary, the voltaic combination is most use- 

 ful when A is greater than L, and indeed it is best constructed of 

 two elements when A is four times greater than L, of three ele- 

 ments when A is nine times greater than L, and so forth. 



27. The circumstance that the current always remains the 

 same at all places, affords us the means of multiplying its ex- 

 ternal action, as in the case when the current influences the 

 magnetic needle. We will, for perspicuity, suppose that, in 

 order to test the action of the current on the magnetic needle, 

 each time a part of the circuit be formed into a circle of a given 

 radius, and so placed in the magnetic meridian that its centre 

 coincides with the point of rotation of the needle. Several 

 such distinct coils, formed of the circuit in exactly the same 

 manner, will, taken singly, produce, on account of the equality 

 of the current in each, equally powerful effects on the magnetic 



