Magnetic properties of permalloy.—Effect of tension on magnetization and hysteresis. Wires of 5 nickel-iron alloys containing 45, 65, 78.5, 81 and 84 percent Ni, 60 cm long and 0.1 cm in diameter, were studied by a ballistic method, for tensions up to 10,000 lb per ${\mathrm{in}.\mathrm{}}^2$ and fields up to saturation (10 to 20 gauss). Permalloy with 81 percent Ni is nearly indifferent to tension in its magnetic behavior; permalloy with less nickel is more easily magnetized and has less hysteresis when under tension, while 84 percent permalloy is more difficulty magnetized and has greater hysteresis when under tension. The saturation values are independent of the tension. In 78.5 percent permalloy, under a tension of 3560 lb per ${\mathrm{in}.\mathrm{}}^2$, saturation is reached at only 2 gauss (and is practically complete at 0.2 gauss) and the hysteresis loss is only 80 ergs per ${\mathrm{cm}}^3$ per cycle, so small that it may be regarded as due to slight inhomogeneity rather than to any essential features of the magnetization process. Relation to crystal orientation. X-ray examination proves that this abnormally low loss is not due to any peculiar orientation of the crystal axes as the crystals are found to be oriented at random. Magnetostriction behavior can be deduced from these results. Above 81 percent Ni, permalloy contracts like Ni while below 81 percent Ni, permalloy expands like Fe.

Demagnetising factor for a wire with a length 600 times the diameter, was determined experimentally and found to vary from a maximum of 1.6×${10}^{-4\mathrm{}}$ to a low value, the changes being like these previously described by Benedicks for iron.

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