OF DENISON UNIVERSITY. 29 



To get the largest current from a battery, its internal resist- 

 tance should be made equal to that of the circuit through which 

 it is to send current. We can readily change the internal resist- 

 ance of a battery if it is convenient to alter the cell arrangement. 

 To overcome the difficulty of making this adjustment in the ordi- 

 nary battery, the device referred to has been found useful in the 

 laboratory. It is described fully in the Bulletin of the Scientific 

 Laboratories of Denison University, Vol. V, p. i6. In explain- 

 ing it briefly here, I will recall several fundamental facts. A bat- 

 tery is arranged /;/ series when its several cells are connected with 

 the positive of one to the negative of the next, so that the whole 

 current traverses every cell ; a battery is arranged in parallel 

 when all its positive plates are connected together, and all of its 

 negative plates together, so that with lo cells, for instance, each 

 cell is traversed by one tenth only of the whole current. In a 

 mixed arrangement several groups of cells, each with parallel ar- 

 rangement, are themselves connected in series. Now with ten 

 cells in series the resistance of the battery is lo times that of a 

 single cell, while with parallel connection only i-io that of a 

 single cell. With mixed arrangement we may secure a variety 

 of intermediate internal resistances. 



The cell-arranger consists of a number of pieces of metal 

 arranged in two rows on an insulating support. Each one is 

 permanently connected by a wire with one pole of a battery cell. 

 The pieces attached to the positive poles (call them abed etc) 

 are in one row, those of the negative poles (call them ;;/ nop 

 etc) in the other. They must be so placed that we can readily 

 make connection by a plug or a switch as follows : a with either 

 b or «, b with either <: or ^, c with d or p etc. Wires for convey- 

 ing the current to the apparatus are attached to ;;/ and to the last 

 piece in the positive row. 



With this accessory, a battery of six to ten open circuit 

 cells, can be made to deliver weak currents at high voltage or 

 may rival the chromic acid plunge battery — which is undoubt- 

 edly the reigning favorite in the laboratory — in giving strong 



