( 91 ) 



Swedish origin whicli lias been investigated l)y H. Backstrom and 

 K. Angstrom ') as to its lliennic and electric condnctivity power. 

 Iji tliis ditrigonal mineral, they found for the qnotient of the thermic 

 conductivity power in the direction of the chief axis (c) and in tiiat 

 perpendicular to it (^/) at 50" : 



^-1.12. 



For the qnotient of the electric resistances w at the same tempe- 

 rature they fonnd : 



— =1.78, and, therefore: - = 1.78. 



lOa Or. 



From this it follows that in the case of the said conductor, the 

 theory agrees with tlie obserxations as to the relation between the 

 conducti\ ity powers only qualitatively, but not quantitatively, and 

 — contrary to the usually occurring deviations — the proportion of 

 the quantities I is smalle v than that of the quantities o. 



Jannettaz's empirical rnle, according to which the conductivity for 

 heat in crystals is greatest j)ai'allel to the directions of the more 

 complete phmes of cleavage, ap[tlies here only in so far as haematite 

 which does not possess a distinct plane of cleavage, may still be 

 separated best along the base |111| (Miller), that is to say parallel 

 to the plane of the directions indicated above with a. 



§ 3. In order to enrich somewhat our knowledge in this respect 

 the })lan was conceived to investigate in a series of determinations 

 the thermic and electric conductivity-power of some higher and also 

 of some lower-symmetrical crystalline conductors, and, if possible, 

 of metals also. For the moment, I intend to determine the quotient 

 of the conductivities in the ditFerent main directions, and afterwards 

 perhaps to measure those conducti\ ities themselves in an absolute 

 degree. 



I. On the thermic and electric conductivities in crystallised Bismuth 

 and in Haematite. 



Measurements of the thermic and electric conducti\ity of bismuth 

 are already known. 



Matteucci ^) determined the thermic conductivity, by the well- 



^) H. Backstrom aii<l K. Angstuöm, Ofvers. K. Vetensk. Akad. Füili. (1888). 

 No. 8, 583; Backstrom ibid. (1894), No. 10, 545. 



•2) Matteucci, Ann. Gliim. et Phys. (3). 43. 4G7. (1855). 



