the vieasurement of Electrical Forces. 387 



described, to make the value of G uniformly constant, the 

 needle for example always pointing to 45°, whatever power 

 of electromotor be applied; and as the sum r-\-'w continues 

 constant, F in the above equation will then vary inversely 

 as -w. The relative force of different electromotors, however 

 powerful or however weak, may thus be accurately measured 

 by the same delicate galvanometer; being inversely propor- 

 tional to the length of that part of the secondary wire con- 

 tained between the wires of the electromotor; or 

 W _'w 



Moreover, if a compound constant battery of three or four 

 pairs be used, and a voltameter be introduced between the bat- 

 tery and the double circuit, it will be easy to find the value of 

 TO answering to a certain F, which is also known in terms of 

 the chemical equivalents decomposed in the voltameter in a 

 unit of time. Thus, the wires being adjusted so as to cause the 

 galvanometer needle to point to 4.5°, note the value of w, viz. 

 the length of the secondary wire contained between the wires 

 of the battery ; note also the length of time required, other 

 things being kept constant, to effect a certain amount of de- 

 composition in the voltameter. The quantity decomposed in 

 one minute, deduced from the above observation by simple 

 proportion, is the F. The product of the F and w thus ob- 

 tained may then be used in the formula 



F'-li?? 



to ascertain the value,— also in terms of chemical equivalents, 

 — of any other force F', without the further use of the volta- 

 meter, and whether the force have energy sufficient for che- 

 mical decomposition or not ; for the quantity necessary to 

 deflect the galvanometer to a certain fixed point is always the 

 same, wiiatever be the inlensitij of the current. 



Thus the same rigorous measurement, in terms of the 

 weight of matter naturally associated with fixed quantities of 

 electricity, may be applied to all electrical forces, whatever 

 their intensity, which the voltameter has applied to those ca- 

 l)abie of producing chemical decomposition, and this by an 

 immediate observation, without the loss of time requisite for 

 a chemical quantitative experiment. 



Since the needle of the galvanometer is liable to slioht 

 changes in the intensity of its magnetism, the above-determit7ed 

 values of F and iso will liom time to time require verification. 



To find the resistance of an electromotor. Let a certain 

 2D2 



