THERMO-ELECTRIC BATTERY. 69 



ducing electric currents. The two kinds of metal 

 conveniently used for this experiment are anti- 

 mony and bismuth, or German silver and brass. 



Were both bars of equal conducting powers, 

 the equal resistance of each would counterbalance 

 the other, and the excitation would take the form 

 of molecular vibrations of the metals, with their 

 gradual heating and expansion. 



For experimental use, small thermo-electric 

 batteries are compactly made with little strips 

 of metal, duly insulated from each 

 other by intervening varnished 

 silk; as represented by Fig. 12. 

 The ends of the conducting wires 

 are inserted in the screw cups x y, Fis ' "' 

 to lead the currents in a circuit around a galva- 

 nometer needle. This is so sensitively affected 

 by the least excitation of heat applied to the con- 

 joined ends of the combined metallic bars, that 

 the combination is denoted a Thermoscope; which 

 is a far more delicate test of heat than any ther- 

 mometer; ~ of i of Fahrenheit being sufficient 

 to move the galvanometer needle. The bars of 

 antimony and bismuth are insulated from each 

 other by varnished silk, with their alternate ends 

 soldered together. This arrangement, for very 

 delicate experimental purposes, is used at a p 

 with a reflector, as represented by Fig. 13, 

 with screens and tubes adapted to exclude col- 

 lateral radiations. To prevent currents of air, the 



