256 A. Schrauf and EF. 8. Dana—Thermo-electrical 
This important fact has been well established in the case of 
gold and iron. 
The variation from + to —, however, has been shown to 
characterize crystallized minerals as well as the amorphous 
metals. Hankel,* Marbach,+ Friedel ¢t and G. Rose|| have in- 
vestigated this subject in relation to the hemihedral crystals of 
pyrite and cobaltite. Friedel first suggested the connection 
between positive and negative thermo-electricity and right and 
left Tem i 
ses seem to be re for its support. or minerals which 
do not crystallize hemihedrally, this hypothesis of Rose is evi- 
dently inapplicable ; and, what is more, if accepted, no varia- 
lized galena positive. 
The thermo-electrical series, recently published by Flight,t 
also affords several such examples. His list embraces a large 
number of minerals. Making hematite 1 (at the negative ex- 
tremity of the series) and fused chalcocite (No. 3) 56 (at the 
positive end), we find, as below: 
Chaleopyrite 1} a No, 2 
Fused ehalnosree ty 21 
Galenite 
4 
Fused galenite 31 
investigated, although this is a point of the highest interest. 
It is clear from the last observations that an explanation is 
often to be found in an altered condition of aggregation. 
; Hankel, Pogg. Ann., vol. xii, 197. + Marbach, Compt. Rend., vol. xlv, 707. 
Friedel, Instit., 1860, 420; Ann. d. Chim., 1869, vol. xvi, 14.” 
G. Rose, Pogg. Ann., 1871, vol. cxlii, 13. : 
5 In a recent paper (which reached us after the completion of our manuscript) 
Friedel (Comptes Rendus, xyi, Feb., 1874, p. 508) claims priority for his views over 
ime he explains that while his hypothesis is to be as- 
hically it of proof. 
Tschermak’s Min. Mittheil, 1872, p. 23. 
enna, 1865, vol. li, 260. 
vol. exxxvi. 
a 
(cael 
Se 
