the Magnetic Properties of Iron. 



251 



as before. The sample is pushed into position in the cradle up to 

 a stop provided for the purpose, where it is held by a brass spring ; 

 when in position its centre of gravity is in line with the two steel 

 points which define the axis about which it may turn, and conse- 

 quently the weight of the sample in no way affects the gravita- 

 tional controlling force to which the pivoted portion of the 

 apparatus is subject. 



The axis of the portion of the apparatus just described is in 

 the same line with the axis of a turn-table of brass, to which the 



Fig. 2. 



Fig. 3. 



permanent magnets providing the magnetic field are bolted ; these 

 magnets are built up of sixteen bar-magnets, placed so as to give 

 a strong horizontal field at right angles to the axis of the turn- 

 table. The turn-table is attached to a wooden stand, and may be 

 turned by means of a nut and screw on the right-hand side of the 

 instrument so as to incline the direction of the field a few degrees 

 to the horizontal either way ; " back-lash " is taken up by a strong 

 spiral spring, which causes the nut to bear always in one direction 

 against its support. One scale of the instrument, the H scale, is 



