ELECTRIC 'FALL.' 



173 



which water flows, for in that case also the pressure of 

 the water gradually and regularly decreases from one 

 end to the other. To express this similarity we will 

 apply to electric currents a term borrowed from flowing 

 liquids, and will call the gradual decrease in the tension 

 the fall in the electricity. 



Let us compare two wires of the same thickness, 

 but of unequal length, a b and c d (fig. 42). If a b 

 is inserted between the poles of a chain, the fall is 

 represented by the oblique line e /. Supposing a b 



FIG. 42. THE ELECTRIC FALL IN DIFFERENT WIRES. 



removed, and c d inserted between the poles of the 

 same chain, the tensions at the ends would be the same, 

 so that the fall in the case of the wire c d may be 

 represented by the oblique line g h. It w r ill be ob- 

 served that in the case of the shorter wire the line runs 

 much more abruptly, the fall is greater, and the cur- 

 rent of electricity advances much more rapidly in this 

 wire. Assuming now that the two wires a b and c d 

 are simultaneously attached to the poles of the chain, 

 in this case also the tensions at the two ends must be 

 equal, but the fall must be different. Supposing that 



