on the Thermoelectrical Properties of Bismuth. 289 



bismuth, antimony, and tellurium, the increase per unit of 

 resistance produced by a magnetizing force of 7660 C.Gr.S. 

 units is 0*20, O006, and O0014 respectively, the corresponding 

 values of the rotatory power are — 4'7, +018, and +790. 



Neither, again, can the change of dimensions produced by 

 magnetization in any of the metals be accountable for the 

 increase of resistance. For though, curiously enough, loading 

 an iron wire increases the resistance, and magnetizing it lon- 

 gitudinally increases the length, whilst loading a nickel wire* 

 decreases the resistance and magnetization decreases the length, 

 yet, according to Joule and others, when an iron wire is loaded 

 to a certain extent longitudinal magnetization begins to de- 

 crease the length ; whereas the author has shown that, even 

 when iron is loaded nearly to breaking, longitudinal magne- 

 tization always produces increase of resistance. Besides, the 

 changes of dimensions in nickel, iron, and bismuth produced 

 by magnetization are far too smallj". Here again, however, 

 it should be noticed that both the decrease of length produced 

 by magnetization and the decrease of resistance produced by 

 loading a nickel wire are considerably greater than the cor- 

 responding increase in the case of iron. 



Whatever it is that causes magnetization to produce so 

 large an effect on the electrical conductivity of bismuth, causes 

 it to produce also a large effect on some of the other physical 

 properties. The thermal conductivity of bismuth is, according 

 to LeducJ and Biglii§, decreased both by longitudinal and 

 transverse magnetization by an amount which is about equal 

 to the amount of decrease produced in the electrical conduc- 

 tivity ; and though it would appear, from Ettingshausen's 

 observations || , that the decrease of thermal conductivity is 

 decidedly less than the decrease of electrical conductivity, yet 

 even this observer makes the former comparable with the 

 latter ; and we shall now see that the thermoelectrical pro- 

 perties of bismuth are quite as largely affected by magnetiza- 

 tion as either the thermal or the electrical conductivity. 



The Thermoelectrical Properties of Bismuth. 

 Sir W. Thomson has shown!" that iron longitudinally mag- 

 netized is negative, and transversely magnetized positive, to 

 iron unmagnetized. Barus and Strouhal** have also investi- 



* See PHI. Trans. 1883. 



t Prof. Barrett failed to detect any change produced in the dimensions 

 of bismuth hy magnetization. 



% Comptes Henclus, 1887. § Ibid. 



|| Annalen der Physik und Chemie, Band xxxiii. (1888). 



If" Electrodynamic Qualities of Metals," Phil. Trans. Part iv. 1856. 



** Bulletin of the U. S. Geological Survey, No. 14 (1885). 





