Measurements have been made of the temperature dependence of the Hall effect in the range 1-300°K, and of the transverse and longitudinal magnetoresistance at low temperatures, in [100] and [111] iron whiskers of high purity (resistance ratios extrapolated to B = 0 ranged from 242 to 852). Analysis of the Hall data shows that both the "ordinary" Hall coefficient Ro and the "extraordinary" Hall coefficient R s vary enormously with temperature, and these variations cannot be explained by existing theories. The theoretical relation R s oc p 2 , where p is the resistivity, does not hold for temperatures below that of liquid nitrogen, and around this temperature Ro, which is positive at room temperature (hole conduction), becomes negative. Ro and R s appear to be isotropic, but at low temperatures these coefficients are extremely sensitive to impurities. The longitudinal magnetoresistance at 4.2 °K shows a large effect of the domain structure on the electrical resistance, which decreases appreciably (46% for the purest specimen) on magnetizing the specimens to saturation. Small negative magnetoresistance (^10%) has also been observed for some specimens in weak transverse fields.

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