The London, Edinburgh and Dublin philosophical magazine and journal of science . he free end, as seen from above,twists in the direction of the hands of a watch. By keepingthe circular field constant, the amount of twist increases atfirst, till it reaches a maximum in a field of about 20 units(fig. 11) ; it then goes on diminishing till it ultimately changesdirection and continues to twist in the opposite direction withincreasing fields. The field at which the twist is reversedincreases with the circularly magnetizing field. In nickel,the direction of twist is opposite to that in iron, but the
The London, Edinburgh and Dublin philosophical magazine and journal of science . he free end, as seen from above,twists in the direction of the hands of a watch. By keepingthe circular field constant, the amount of twist increases atfirst, till it reaches a maximum in a field of about 20 units(fig. 11) ; it then goes on diminishing till it ultimately changesdirection and continues to twist in the opposite direction withincreasing fields. The field at which the twist is reversedincreases with the circularly magnetizing field. In nickel,the direction of twist is opposite to that in iron, but thegeneral feature is similar to iron, the only difference beingthat even in strong longitudinal fields the twist is not wires of equal thickness, the amount o£ twist in nickelis greater than in iron—the maximum twist in iron wire 62 Prof. Nagaoka and K. Honda on Magnetostriction of 1 mm. diam. by passing 6 amperes through it amountsto about 28 per cm., while with nickel wire of 083 under similar conditions, the maximum twist amountsto about 200. Fig. 5(0 j5 Three different kinds of nickel-steel wires, for which ourthanks are due to Dr. Ch. Ed. Guillaume, were tested. Theresults of the measurements are shown in fig. 12. The sense in which a nickel-steel wire twists is the sameas for iron. The amount of twist increases with the magneticfield, but it soon reaches a maximum, to decrease afterwardsquite slowly as the field becomes stronger ; and the twist isgenerally reversed in high fields. With the specimens tested,the twist increases with the percentage of nickel. The23*6 per cent. M and 39*2 per cent. ]STi were examined ina hard drawn state ; but the 45*2 per cent. Ni wirewas examined after annealing it in hydrogen, as alreadydescribed. Twist by varying the circular field.—In iron the twi^tincreases with the strength of the circular field if the longi-tudinal field remains constant. Such is also the case withnickel in moderate and strong fields. Jn l
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