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 interruptor, 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 interruptor, 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 interruptor 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 interruptors, 
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 tndhiraeite pie by the deflagrator—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 
soon 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 silationn: 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 3s 
