282 Copper Mines. 
notus is confined, they @// receive a shock of greater or less 
tensity when the fish discharges, proving that all the con- 
ducting matter round the fish is filled at the moment with 
eirculating electric power, resembling generally in disposi- 
tion the magnetic curves of a magnet. The Gymnotus 
feeds on other fish, which it kills by giving them a shock; 
this it does by forming a coil round the fish, so that itshould 
represent a diameter across it. Living, as the Gymnotus 
does, in the midst of such a good conductor as water, it 
seems at first surprising that it can sensibly electrify any- 
thing; but, in fact, it is the very conducting power of the 
water which favours and increases the shock by moistening 
the skin of the animal through which the Gymnotus dis- 
charges its battery. 
The Silurus electricus—This fish is found in the Senegal, 
the Niger, and the Nile. It is about 20 inches long. The 
shock is distinctly felt when it is laid on one hand, and 
touched by a metallic rod held in the other. Its electrical 
organs are much less complicated than those of other 
electrical fishes. Other known electrical fishes are the 
Tetraodon electricus, found in the Canary Islands, and the 
Trichiarus eleetricus, which inhabits the Indian Seas; 
several others have been met with, but not hitherto accu- 
rately described.—Student's Texrt-book of Llectricity. 
COPPER MINES.—No. I. 
EW books of a popular character have been‘written 
upon mining; so that persons have rarely the means 
of acquiring any information as to the nature of mines, the 
modes by which ores are extracted from the earth, or the 
preparations which they undergo prior to their being 
brought to a state of use. The most superficial knowledge 
of these things would have deterred many from specula- 
tions, which experience has proved they ought to have 
avoided ; and to which they were lured by a phantom en- 
gendered by their cupidity and magnified by their igno- 
rance. 
Every one knows that the metallic substances chiefly 
in use are gold, silver, copper, iron, lead andtin. Of these, 
the two former have never been found in any parts of 
Great Britain in sufficient quantities to warrant a con- 
