460 



Prof. D. E. Hughes. 



[May 27, 



quently all measurements taken wherein this separation is not com- 

 plete, gives the result of a mixed effect. 



In the method which I have described, the separation of the extra 

 current from the momentary primary current is so complete that the 

 measures given by the induction balance and resistance slide are 

 invariably the same for a given wire ; there is no personal equation, 

 for all observers find precisely the same values both for the resistance 

 and for the extra current. 



The method is, however, defective in measuring any small diffe- 

 rence of resistance in the variable period in copper wires, as the 

 induction balance itself introduces an additional but opposing resis- 

 tance by the approaching of its coils, consequently any resistance 

 which we observe is a fraction less than the real amount. To prove 

 this we have only to use a balancing induction current produced from 

 the battery circuit, as shown in my first paper, when we observe 

 this small difference, and better, observe any small difference of 

 resistance in a straight copper wire, and greater when the wire is 

 formed into a coil. 



Soft iron wire gives a far higher resistance in the variable period 

 than hard iron, but each wire, according to its molecular structure, 

 has its own value ; the effect increases with the diameter, ranging 

 from 25 per cent, increase of resistance for wires of 2 mm. in diameter, 

 to 500 per cent, for those of 6 cm. 



Table II. — Resistance of Iron and Copper in the Stable and Variable 



Periods. 



Wires, 1 m. in length, 

 5 mm. in diameter. 



Comparative 

 force of the 

 extra 

 current. 



Resistance 

 in ohms, 

 stable 

 period. 



Resistance 

 in ohms, 

 variable 

 period. 



Percentage 

 of increased 

 resistance in 

 variable 

 period. 



Soft Swedish iron .... 



American compound 

 wire, copper exte- 

 rior, steel interior. . 



Ditto, steel exterior, 

 copper interior 



78 

 234 



| 83 

 | 213 



0-001284 

 '008346 



-002247 

 -007750 



-001372 

 -022200 



-002696 

 0-0248000 



7 



166 



20 

 220 



Table II shows a few illustrative examples : the resistance is given 

 in the fractions of the ohm, indicated by the resistance slide M, upon 

 the supplementary resistance wire HI. 



The table shows that copper and the American compound wire 

 coated with copper have an extremely rapid action or curve from an 



