TOESION AND MAGNETIZATION. 



265 



definite quantitative results. The position of maximum twist 

 in nickel shows a large difference in the present from the corres- 

 ponding experiment by Dr. Knott. 



The twist produced by longitudinal magnetization of a cir- 

 cularly maojnetized wire was measured in the followin"' way. To 

 the extremities of an iron or nickel wire 21 cm. Ions; were 



brazed stout brass wires, and a 

 light plane mirror was attached 

 to the lower one. The end of 

 the lower brass wire was dipped 

 in a mercury pool, while the 

 upper brass Avire was clamped to 

 a small tripod, which rested on the 

 top of a magnetizing coil pro- 

 vided with hole, slot, and plane 

 arrangement. One end of the 

 accumulator Avas connected Avith 

 the tripod, while the other was 

 led to a mercury pool. The 

 wire hung vertically in the axial line of the coil, which was 

 30 cm. long and gave a field of o7.1'7 C.G.^. units at the 

 centre by passing a current of one ampere. The vertical com- 

 ponent of the terrestrial magnetic field was compensated by plac- 

 ing another coil in the interior of the magnetizing coil. The 

 lower part of the wire to be tested Avas protected against air 

 current by enclosing it in a Avide brass tube with a small win- 

 dow^, just where the reflecting mirror was attached. The twist 

 was measured by scale and telescope method, by which the 

 deflection of 0.3" per. em. was easily read. The current Avas 

 measured by Kelvin graded amperemeters, whose constants were 



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