Section III., 1908. [81] Trans. R. S. C. 



IV. — Nate on the Temperature Variations in the Specific Resistance of 



Heusler's Alloys. 



By H. A. McTaggart, M.A., and J. K. Eobertson, M.A. 

 (Communicated by Prof. J. C. McLennan, and read May 26, 1908.) 



Introduction. 



The following note contains an account of a preliminaij study of 

 the specific resistance of several samples of the bronze alloys discovered 

 à few years ago by Ileusler.^ There already exists as a result of the 

 investigations of various experimenters, a considerable amount of in- 

 formation with regard to the nature and properties of these alloys, 

 but no careful examination of their electrical resistance has up to the 

 present been attempted. 



A perusal of the literature bearing on the subject of Heusler's 

 alloys shews a number of strildng contrasts between their properties 

 and that of many other alloys, as well as pure metals. They are mag- 

 netic, though composed of non-magnetic constituents ; their permeability 

 shews unusual variations accompanying the processes of cooling from 

 high temperatures ; their hysteresis effects depend on similar treatment ; 

 and they exhibit magnetostriction phenomena altogether different from 

 those displayed by other well known magnetic substances. Consideration 

 of these properties, and particularly of those which are subject to modi- 

 fications by specific heat treatment, suggested the possibility of the 

 existence of peculiarities in the values of the coefficient of resistance in 

 some regions of temperature. 



It became then a matter of interest and importance to examine the 

 resistance of these alloys, not only at ordinary temperatures buii also 

 over as wide a range as possible, so as to observe as fully as may be 

 the character of any variations which might occur in the specific resist- 

 ance in consequence of temperature changes. To add, then, if possible, 

 from this. line of investigation, some further data which might help to 

 explain the ma.çrnetic properties of these bronzes, the authors, at the 

 suggestion of Prof. McLennan, carried out as time permitted, the series 

 of observations described below. 



'Verb. d. Deut. Phys. Gesell, 5,219, 1903; Marburg Schriften, 237, 1904; 

 Ann. d. Phys., 16,535, 1904; Electrician. June 16tb, 1905; Pbys. Rev.. 96,335, 

 1905: Verb. d. Deut. Pbys. Gesell, 7,133, 1905; Proc. Roy. Soc, 76,271, 1905; 

 Pby.s. Rev., 23.498, 1906; Bulletin of Bureau of Standards, Wasbing-ton, Vol. 

 12, No. 2, p. 297, Aug., 1906; Verb. d. Deut. Phys. Gesell, March, 1907; Pbys. 

 Rev., 24, 1907; Verb. d. Deut. Phys. Gesell., Jan., 1908. 



