530 Mr. L. Schwendler on the General Theory 



tionary, and adjust balance by altering the resistance in one or 

 both of the two circuits, or leave the resistances constant and 

 alter the relative position of the two coils or their armatures 

 with respect to a given magnetic pole. These two methods of 

 readjusting balance shall be considered separately. 



a. Readjustment of balance by altering resistances. 

 In order to have immediate balance it will be clear that the 

 alteration of resistance must be restricted to the compensation 

 circuit, which is electrically independent of the line-circuit. 

 The total resistance in the compensation circuit consists of 

 three different resistances, namely b, a, and d. Neither b nor 

 a, considering their nature, can conveniently be made adjust- 

 able in practice ; hence the alteration of resistance in the com- 

 pensation circuit is restricted to d, which must therefore con- 

 sist of increments of the proper size. The adjustment of d 

 should be quick and convenient. 



E 



In addition to this adjustment, \= — may be made adjust- 

 able by varying E in increments of one cell. Such an adjust- 

 ment, however, is not fine enough for ordinary use ; the elec- 

 tromotive force of one cell is too large a quantity in compa- 

 rison with the total electromotive force used in the compensa- 

 tion circuit. If the variation of the line-current becomes very 

 great, it might perhaps be found convenient to alter E ; but as 

 an ordinary mode of adjustment it must be dispensed with *. 



It is scarcely needed to point out that to adjust balance by 

 altering the line-current, either by varying the resistance or 

 the electromotive force f or both of the line-circuit, must be 

 rejected once for all, because such an adjustment of balance in 

 the one station could never take place without disturbing the 

 balance of the other station, or, in other words, the required 

 immediate balance could not be fulfilled. 



b. Readjustment of balance by moving the coils or armatures. 



If we suppose both the coils or their armatures simultane- 

 ously movable in the same direction, then clearly this mode of 

 adjustment contains not only the required immediate balance, 

 but in addition represents also a very rapid and entirely con- 

 tinuous action. For this reason it is apparently preferable to 



* During the period of low insulation of the line it might be advisable 

 and practicable to make E larger than during the period of high insulation 

 of the line (wet and dry seasons). 



t Alteration of electromotive force of a galvanic battery cannot be 

 achieved without altering its internal resistance. Hence varying e would 

 also involve a variation of /3; and in order to keep/=w-f fi, it would be- 

 come necessary to alter w simultaneously with e ; i. e. w would have to be 

 increased when e decreases, and vice versa. This method, besides being 

 rough, would therefore be also inconvenient. 



