MAGNETIZATION AND MAGNETIC CHANGE OF LENGTH. 3 



rods, each end of the ovoids entering about 2 mm mto the rod. 

 The upper piece is connected with a wire 

 stretched vertically, and the lower piece is 

 screwed to the bottom of the specimen-holder, 

 as shown in the annexed cut. The axis of the 

 ovoid can be adjusted by three small screws. 

 The holder was made of a copper tube, with 

 — " three long slits, equally distant from one ano- 



ther, along its axis. These slits permit the 

 adjustment of the specimens to the axial line of the tube. The rest 

 of our apparatus was exactly the same as in the former experiment. 

 In the present experiment, the magnetization was, at the 

 same time, measured by the magnetometric method. The mag- 

 netometer consisted of a bell-shaped magnet suspended by a quartz 

 fibre in a thick copper case. A magnetizing coil (length =40 cm, 

 4/T?z= 394.4) and a compensating coil of nearly the same dimensions 

 were placed respectively due magnetic east and west of the magneto- 

 meter. The magnetometer was placed in such a position that the 

 specimen exerted the maximum effect upon it. The vertical com- 

 ponent of the earth's field was compensated for. The deflection of 

 the magnetometer was measured by means of a scale and telescope. 

 In measuring magnetization, the following precautions were 

 taken. The verticality of the two coils was tested by means of 

 a level. The line of the magnetometer, the compensating coil 

 and the magnetizing coil, was then tested by a compass needle. 

 The compensation of the earth field and then that of the mag- 

 netizing coil were next effected ; lastly the scale and telescope 

 w^ere placed in correct positions. 



The precautions above enumerated were especially necessary, 

 as the magnetization and the magnetic hysteresis in strong fields 



