Effect of Stress on Magnetization. 69 



at both its ends to thick rods of brass. The whole was hung* 

 vertically in the axial line of the magnetizing coil, and 

 consequently of the secondary coil, the upper rod being 

 firmly clamped to the rigid frame above the coils. To the 

 end of the lower rod a hook was attached ; from this hung 

 a flexible cord which, after passing through a system of two 

 pulleys, was stretched by a weight, without imparting any 

 injurious pendulum motion to the specimen. Near the end 

 of the lower rod, a rigid pin was screwed on perpendicular to 

 the rod. The ends of the pin fitted to the two V-shaped 

 grooves cut lengthwise and diametrically opposite to each 

 other on the inside of a brass cylinder, which could be turned 

 about a fixed vertical axis to any desired angle. The angle 

 of twist was read by means of a graduated circle and the 

 index attached to the torsion cylinder to ^ of a degree. In 

 the experiment of the tension effect, the above arrangement 

 served to prevent any accidental twisting of the specimen 

 without causing a sensible friction to the stretching. 



§ 2. Method of Experiments. 



Our procedure was usually made in the following order : — 

 The direct effect of the magnetizing coil on the galvanometer 

 was tested first of all. The specimen was removed, the 

 secondary circuit opened, and the maximum current was 

 passed through the primary. If there were any constant 

 deflexion of the galvanometer-mirror, the observer signalled 

 to the experimenter, who adjusted the orientation of the 

 compensating primary coil till the deflexion on breaking, 

 making, or reversing the current was brought to zero, 



Next the secondary circuit was closed, a strong current 

 was passed through the primary, while the observer was 

 watching the galvanometer ; the compensating secondary 

 was slid within the primary till the ballistic deflexion was 

 reduced to zero. 



Next the compensation for the earth field was effected. 

 For this purpose, the specimen was introduced into the 

 magnetizing coil, clamped firmed and stretched by a suitable 

 tension, care being taken to place the wire co-axially with the 

 coils. The specimen was carefully demagnetized by reversals ;. 

 the secondary was closed, a weak field excited in the primary, 

 and the consequent deflexions noted. After a complete 

 demagnetization, the same magnetizing current was passed in 

 the opposite direction. If the two corresponding deflexions 

 of the galvanometer were not equal to each other, the 

 resistance in the compensating circuit was so adjusted, that 



