observed in some Metalliferous Veins. 277 



copper, lead, and iron, when unequally heated, are traversed by 

 currents of electricity of very low intensity, although in con- 

 siderable quantity. 



In a communication to the Royal Geological Society of Corn- 

 wall, in 1834, Mr Fox states, that when heated, copper pyrites 

 was positive both to purple and vitreous copper-ore, to galena, 

 and to iron pyrites ; also that elevation of temperature induces 

 positive electricity in the sulphurets of copper and lead, but ne- 

 gative in iron pyrites. 



It is well known that u foreign metals brought into contact 

 with a homogeneous circuit near the point of heat, participate 

 in the action, and tend to determine the current."" (Prideaux, 

 Phil Mag., 3d series, 1833, III. p. 272.) Seeing the compli- 

 cated results, obtaining when a.few metals only are employed, 

 could we expect simplicity where so many more elements enter 

 our circuit ? 



We have seen that the contents of our veins consist of seve- 

 ral ores of many metals : who would venture to predict the di- 

 rection of a thermo-electric current excited in such a mass ; the 

 elements varying in the numbers, magnitudes, and directions of 

 their masses ; in some places connected, in others disjoined ; here 

 mixed, there separate ; in one spot coincident, in another oppo- 

 sing ; parallel in some situations, transverse in others ? It is ob- 

 vious that the higher temperature of the slate than of the gra- 

 nite, and of masses of ore dipping from the latter towards the 

 former are highly favourable conditions for the development of 

 thermo-electricity ; and in order to see how it accords with facts, 

 we will assume a case which shall involve them all. 



Suppose a mass of copper-ore originating near the surface in 

 slate, to be prolonged in extent towards, or into the granite, the 

 upper portion would probably be in general copper-pyrites, the 

 lower vitreous copper-ore. On a given liorizontal line, we shall 

 then have the positive ore (the pyrites) in the warmer rock, and 

 the negative (vitreous) in the colder ; and the same result will 

 obtain, whether each ore singly had been unequally heated, or 

 whether both are in contact at the same temperature. In either 

 case a current would be determined towards the granite. 



If, however, we take a vertical line, our conditions are differ- 

 ent ; for here, if the points be distant, the higher temperature 



VOL. XXII. NO. XLIV. APRIL 1837. T 



