Elasticity of Ferromagnetic Substances by Magnetization. 39 



light mirror with a suitable counterpoising. The lower rod 



flexible band / made of a 

 bundle o£ very line cop- 



for the magnetic wire carried a 

 Fiu-. 1. 



a. n 



c\ I; 



'•i 



Te 



Cu 



per wires, which pressed 

 the axis of the mirror 

 lightly upon the plane 

 vertical side of the car- 

 riage. To the lower ends 

 of these rods, a flexible 

 silk cord was attached ; a 

 pulley p hanging in this 

 cord was pulled vertically 

 downward by a weight. 

 The friction- wheel q served 

 to adjust the distance be- 

 tween the two vertical 

 wires. Instead of hanging 

 the weight directly, a sys- 

 tem of pulleys g li was 

 used in order to avoid any 

 injurious shock accom- 

 panying the loading and 

 unloading of the wires. 

 When the elongations of 

 the two wires due to ten- 

 sion were exactly equal, 

 there was of course no 

 rotation of the axis of the 

 mirror. If, however, the 

 compensation were dis- 

 turbed in any way. the rotation could be observed in the 

 usual manner by means of a vertical scale and a telescope. 



To increase the sensitiveness of the arrangement, a wire 

 about 74 cm. long was used ; for want of a sufficiently long- 

 coil, two coils of the same dimensions were used, placing the 

 one above another. The length of each coil was 39*90 cm.. 

 the internal diameter 5*80 cm., and 47r/t = 39o'5. The air 

 gap between the two coils was only I'V cm., so that the 

 heterogeneity of the field in this space was inconsiderable. 

 The wire to be tested then lay nearly in a uniform field. 



The compensating copper wire was chosen of such dimen- 

 sions as to produce an elongation nearly equal to that of the 

 specimen. The final compensation was always made by 

 properly adjusting the distance between the two knife-edges 

 supporting the horizontal beams, from which the wires were 



suspended. A 



certain weight 



was added to the pan, or 



