ELECTRO-MAGNETIC INSTRUMENTS. 27 



Fig. 446. Fig. 447. 



each, are then placed within the double copper vessels ; the 

 holes in the bent wires, being hung upon the uppermost 

 pointed ends of the vertical wires, before mentioned. 

 Diluted acid being then poured into the space between the 

 copper cylinders, the voltaic action commences, and presents 

 the phenomena of the cylinders revolving upon their axes, 

 the copper vessels revolving in opposite and contrary direc- 

 tions, and the zinc cylinders turning in opposite directions 

 to them ; the rapidity of their revolutions depending upon 

 the strength of the acid, and the delicacy of their sus- 

 pension. 



The zinc cylinders revolve with rapidity, but from the 

 superior weight of the copper cylinders, when filled with 

 the exciting liquor, it is rarely that the rotatory tendency 

 can be exhibited in them. Price, $6.00. 



Revolving Cylinders. (Fig. 447, as above.) A horse- 

 shoe magnet is supported vertically upon a stand, having 

 holes formed in the centres of its ends. Two wooden 

 circular troughs are secured by binding screws upon the 

 arras of the magnet, to contain mercury. Into the holes 



