BETWEEN LOXGITUmXAL AND CIRCULAR MAGNETIZATIONS. 287 



was wouud on a glass tube of external diameter 0.748 cm. with 

 fine copper wire, and placed in the magnetizing coil, in the axial 

 line of which the wire was placed. The wire was soldered to 

 a brass wire (2 mm. in diameter and 10 cm. in length) at each end, 

 through which longitudinal current entered or left the wire. 

 The ballistic throw produced by passing a given longitudinal 

 current gave the change in magnetization. 



The smaller iron tube was not circularly magnetized l)y 

 means of a current passing directly through the tube, Ijut was 

 placed in the magnetizing field due to a current through an in- 

 sulated copper wire of 1.8 mm. diameter in the axial line of 

 the tube. To avoid heating, cold water was kept constantly 

 flowing through the interspace between the wire and the inner 

 wall of the tube. 



To measure the effect of longitudinal current on uiagneti- 

 zation by the magnetometric method, we must eliminate tlie direct 

 action of the current on the magnetometer. For this purpose, 

 another copper wire of the same diameter was bent so as to form 

 a rectangle 6 cm. by 3('). This wire w^as fixed in the horizontal 

 plane passing through the centre of the magnetizing coil, with 

 , its longer sides parallel to the central line and 



symmetrical wdth respect to the centre of the coil 

 as shown in the annexed figure. The central 

 copper wire laid on V-shaped grooves of brass 

 plates B and B' at the ends of the coil, and its 

 terminals were dipped in small mercury pools, 

 bored in the middle of these grooves. On the 

 side of the magnetometer, a short copper wire 

 W (1 cm. in length) was placed parallel to and 

 under the central copper wire to connect the middle point 



O 



