GALVANIC INSTRUMENTS. 



Fig. 390. 



331 



Mmmm\ 







Van Melseus Battery. (Fig. 390, as above.) This cut 

 represents a useful arrangement of copper and zinc plates 

 for a galvanic battery ; the copper soldered to the zinc in 

 each pair envelopes the zinc of the following pair, so as to be 

 exposed to the two surfaces of this plate, but without being 

 in contact with it. It differs from Wollaston's battery in 

 having the metallic plates much nearer to each other ; they 

 are only about one-twelfth of an inch apart, and are main- 

 tained thus by small pieces of cork interposed between the 

 plates of zinc and those of copper ; while the plates of cop- 

 per of the consecutive elements are separated by squares of 

 glass of the same size as the plates ; all the squares are 

 placed in a wooden frame (represented in the cut), whk-,h is 

 well varnished, in which they are easily retained, without it 

 being necessary to attach them by screws to a bar of wood, 

 as in the case of Wollaston's. Price, 25 pairs, $20.00. 



The Cylindrical Pot Battery. (Fig. 391, next page.) 

 The cylindrical pot battery consists of a double cylinder of 

 copper, with a bottom of the same metal, and a movable 

 cylinder of zinc, between the copper cylinders; the zinc 

 cylinder is supported by three branches. The branches are 

 covered with wood to insulate them from the copper, and 

 are formed in the shape of rollers, with grooves entering 



