and Iron Wires placed in Strong Magnetic Fields. 127 



pieces at about 7 mm. apart, tut for fields reaching up to 

 30,000 c.G;S. units, the pole-pieces were about 2 mm. apart. 



(3) Results. 

 The fractional change of resistance A<£ in the specimen 

 examined corresponding to the step A# on the bridge-wire 

 is calculated from the formula 



., AN_R + S Q 



a *=it-r7s-n- <7 - a ' e; 



where <x = resistance of bridge-wire per unit length ; 

 N = resistance of the specimen examined. 

 Q = total resistance in the bridge-gap containing the 

 specimen. This includes the resistance of the 

 compensating coil and the connecting wires 

 and cables ; 

 Rand S = resistances of the auxiliary coils. 



Three experiments were carried out : — 



Experiment I. with three pieces- of nickel wire in series, 



diam. -0206 mm.* 

 Experiment II. with two pieces of nickel wire in series, 



diam. '0159 mm. 

 Experiment III. with two pieces of iron wire in series, 



diam. -0208 mm. 



Table I. — Particulars of coils, &c. used in the 

 experiments. 





Expt. I. 



(18°-5 C.) 



Expt. II. 



(17°-5 0.) 



Expt. II L 



(17°-5C.) 



Resistance of specimen in ohms 



Resistance of auxiliary coil R 



0-761 

 0-615 

 0-506 

 0-324 

 1-240 



0-0132 

 18-01 



0-835 

 0-615 

 0-492 

 0-4-13 

 1-506 



0-0132 

 16-47 



0-916 

 1-527 

 1-231 

 0-444 

 1-530 



0-0132 

 6-28 



Resistance of auxiliary coil S 



Resistance of compensating coil 



Total resistance in gap E containing 

 specimen 



Resistance of 95'5 cm. of bridge wire . 

 Maximum step in cm. ■(# — ,r ( )) 





* The nickel and iron wires were supplied by Messrs. Hartmann $l 

 Braun, Frankfurt. 



