358 On the use of the Dynamic Multiplier. 



its metallic form. Pairs of plates of copper and iron, copper and 

 lead, lead and zinc, or iron and zinc may be used, but copper and 

 zinc are preferable.) As a still further improvement in the revolv- 

 ing interrupter, I have attached a short shaft to its axis, which car- 

 ries two wheels, one entire and one stellated. A small battery is 

 used to move the interrupter, while the circuit of the battery used 

 with the coil is broken by the star wheel of the attached shaft ; the 

 entire wheel turning in mercury preserves the connexion. The ve- 

 locity of this interrupter is very great, and when viewed in the night 

 by its own light, the whole apparatus appears to be at rest. When 

 decompositions are performed with the multiplier and interrupters, 

 the acidulated water is put in a glass tube, with platinum wires pass- 

 ing in at the ends and running parallel to each other for an inch or 

 two, and about one fourth of an inch apart. A fine tube passes 

 through one of the corks to allow the water to escape. Fine wires 

 answer better than large. 



On the thermo-electric spark and shock. — The six outer circles 

 of the dynamic multiplier, connected with a single thermo-electric 

 pair, give a bright spark, when the circuit is broken with a clean 

 pencil of zinc or lead. The snap is very audible, and the shock dis- 

 tinct, by acupuncture. 



Ignition of anthracite coal by the dejlagrator. — Anthracite be- 

 comes a good conductor when heated, and becomes intensely ignited 

 between the poles of the deflagrator, if the following method be 

 adopted. Pencils of the coal being-attached to the poles, the ends 

 of a piece of copper wire bent in the form of the letter U are pla- 

 ced on either side just where the coal is in contact with the poles ; 

 ?the wires are then slowly approximated on the coal points, which 

 :seon glow with a brilliant white light, and afford a short arch. 



On the use of the metals as substitutes for copper in batteries 

 ■excited by the cupreous salts. — As the copper plate serves only for 

 a conductor of the electricity put in motion, any metal having the 

 same electrical relation to zinc as copper, must be an equivalent, 

 provided its conducting power be as good ; but where plates of metal 

 of no great length are used, this difference must be inappreciable. 

 The activity of such batteries is commensurate with the decompo- 

 sition of the metallic salt ; and as iron or lead precipitates metallic 

 copper from its solutions, the decomposition in the batteries might 

 be facilitated by the introduction of these metals. As the results of 

 a number of experiments, I conclude, that iron when clean and 

 freshly immersed in sulphate or nitrate of copper with zinc. Is as 



