and Iron Wires placed in Strong Magnetic Fields. 12 5 



stream of cold water was passing. This precaution was 

 taken to prevent any heat radiation from the lamps to the 

 bridge connexions. 



The battery circuit consisted of one small storage-cell in 

 series with a resistance of 150 ohms, and a mercury key. 

 The current was allowed to flow through the bridge for 

 about an hour before any readings were taken, and it was 

 not stopped until the set of readings was over. This was 

 done in order that the rise of temperature due to the passage 

 of the current through the specimen might have attained 

 a steady value when the readings were being taken. 



The electromagnet was situated broadside on to the 

 galvanometer, and at a distance of about 45 feet from it. 

 In this position and at this distance, it was found that the 

 field due to the magnet did not affect the galvanometer 

 needle. The specimen examined and the platinum wire were 

 connected to the bridge table by means of three lengths of 

 thick cable twisted together and passing from the table over 

 the beams of the laboratory to three terminals on a wooden 

 upright fixed to the frame of the magnet and insulated from 

 it. The cables were twisted together to prevent inductive 

 effects when the wires moved in the earth's field. 



The specimen was held in position in the field as shown in 

 fig. 3 a. A thin piece of ebonite, thickness about 1 mm., 



fS*^*-^**^*}*^. 



Fig 1 . 3 a. Fig. 3 b. 



T : Terminals on wooden upright attached to frame of magnet. 



was cut into a rectangle 6 cm. by 1 cm. Two strips of 

 copper were fixed to each side of the ebonite, and three 

 pieces of the specimen examined were soldered across the 

 ends of these as shown in tig. 3 b. Great care was taken to 

 solder them straight across and parallel to one another. The 



°[\^o 



