in Metalliferous Veins. 7 



Deviation 63'' ; temperature not observed. The disc on 

 galena having been heated, the deviation was somewhat di- 

 minished ; the other on pyrites being heated, there was an in- 

 crease to 64^. 



The original temperatm-e of the discs was determined by 

 thei'mometers placed in a sort of case bent from the discs 

 themselves. 



These instances prove manifestly, that the great effect by 

 an originally very slight difference of temperature, cannot even 

 be attributed to the same cause as the feeble effect produced, 

 when the discs are strongly heated. When the points con- 

 nected with the multiplicator belong to the same mass of ore, 

 the heating has totally different effects ; to which case we now 

 px'oceed, — 



II. Tivo ore-poi}tts in uninterrupted metallic connection with 

 one another, induce no electrical current through a wire con- 

 necting them. 



Although it is often impossible positively to assert of two 

 ore-points, that within the rock there does not exist an un- 

 interrupted metallic connection, it is, on the other hand, also 

 far from a simple matter to find two points of which it can be 

 said undoubtedly that no fine rent or cross course separates 

 them. Although, therefore, I connected several pairs of points, 

 which were, in all probability, in uninterrupted metallic con- 

 tact, 1 can only say so with pei-fect certainty of two that I 

 chose on the 5th drift of Frisch Gliick, which were only 4'" 

 apart in massive galena. At first, a deviation of 4° was ob- 

 tained in the direction from the point a towards b ; b v/as then 

 gently heated, the current instantly changed direction, going 

 from b towards a, and causing a deviation of 20^. A gently 

 heating of a reversed the current again to the direction from 

 a towards b : mere contact with the hand caused a deviation of 

 10'. Although the natural temperature of the mass was 20' C. 

 (60° F.), we see from this, how great was the sensibility of the 

 whole apparatus to slight differences of temperature, when the 

 intervening distance was short and the points in unintennipted 

 metallic contact. Manifestly, the deviation of 4", observed at 

 the commencement of the experiment, was only a consequence 



