OF FERROMAGNETIC WIRES BY MAGNETIZATION'. 5 



corresponded to an elongation or contraction of 5.13x10'' in one 

 case and 2.72x10"' in the other. As xVth of the micrometer scale 

 can be easily observed, a dilatation of 0.6 x lO'*^ per cm. was accurately 

 measured in the latter case. 



3. Observations were conducted accordino^ to the foUowins" 

 method. The wire to be tested was hung vertically and stretched by 

 a weight of 5 kilograms for 3 or 4 hours to make it straight. To 

 begin with, all the weights were once taken away, and again loaded 

 with a weig-ht of 0.5 or 1 kiloo;ram. After one or two hours, the 

 observations were completed in the following order. The wire was 

 first demagnetized, and then magnetized by passing successively 

 increasing currents and the corresponding deflections taken, the 

 demagnetization being repeated before each magnetization. A set of 

 observations being thus taken, successively increasing loadings were 

 applied and the corresponding sets of observations noted. The obser- 

 vations were, for the most part, taken at night to avoid small 

 disturbing vibrations of the wire due to the shaking of the laboratory 

 building. 



Since the resistance of the mao^netizing- coil was onlv 0.6Q, the 

 thermal expansion of the suspended wire due to the heating of the 

 coil was negligibly small for the current used in the present 

 experiment ; but for safety, the deflection was taken as soon as 

 possible. Substituting for the steel cylinder a brass one of the same 

 thickness, exactly the same results were obtained, showing that tha 

 influence of the magnetic action between the coil and the steel cylinder 

 is insensibly small. 



When the pressure in the contact surface between the cylinder 

 and the wire was moderate, repeated applications and removals of the 

 magnetizing field showed no trace of slipping in the cylinder. 



The wires tested had the followin»- dimensions : — 



