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bottom to a little beyond balf the length of the copper 

 cylinders, care being taken to prevent the zinc from touching 

 the copper tube in which it is inclosed: they are kept separate 

 by small bits of cork. Each copper tube and its enclosed 

 zinc forms a galvanic pair, and these are joined by wires in 

 sequence or series as before described, viz., the first zinc to 

 the second copper, the second zinc to the third copper, and 

 so on to the end of the series, excepting the last zinc, which 

 has no metallic connexion with any copper tube, its wire 

 projects for the purpose of attachment to the main wire or 

 conductor conveying the electricity to the rock; the first 

 copper tube is in like manner unconnected with any zinc, and 

 has a similar projecting wire for attachment to the main con- 

 ductor. These terminal tubes or their wires are called poles ; 

 that of copper is the positive, and that attached to the zinc 

 the negative pole. 



All these cylinders, insulated from each other, are placed 

 in a frame suspended by an excentral axis, somewhat in the 

 same way that a mirror is hung on its frame, the cylinders 

 contain sulphuric acid and water, in the proportion of one 

 part acid to sixteen of water, and when the battery is not 

 in action, the ends of the copper tubes containing the zincs 

 are uppermost ; the consequence is that the exciting solution 

 falls to the bottom of the copper tube, and is thus removed 

 from contact with the zinc, but when a current of electricity 

 is wanted, the frame can be reversed by pulling a string, the 

 dilute acid falls upon the zinc tubes, and the battery is thus set 

 in action ; to stop the current of electricity, the frame is 

 turned into its original position, and the zinc tubes removed 

 from the exciting solution. By this contrivance we obtain the 

 full efifect of the first immersion of the plates in dilute acid, 

 which, it is well known to electricians, is in a manifold degree 

 greater than any effect that can afterwards be obtained ; 

 so much is gained by this, that for ordinary purposes of 



