40 



Laws of the Elementary Voltaic Battery. 



two pillars 36 inches high. A strong tube of J inch diameter, is 

 secured at its upper extremity in the center of the circle A, passes 

 through the brace D, and terminates an inch and a half above the 

 lower circle B. The coil, consisting of 100 feetof jSne copper wire 

 wrapped with silk, rests partly above, partly in a groove beneath the 

 circle B, passing through two holes immediately at the base of the 

 pillars. The tube extends just through the coil, and assists to sup- 

 port it. 



Fig. 1. 



The needle is suspended by a torsion filament of glass, represented 

 more fully in Fig. 2. The upper extremity of the tube receives a 

 glass stopper, formed of a portion of thick capillary tube, filed into a 

 shoulder, and made to fit easily into it. The upper end of the glass 

 filament is made fast in the capillary bore, while the lower end is ce- 

 mented into a short piece of fine straw. The needle (a fine knitting 



