On the use of the Dynamic Multiplier. 355 
into a flat spiral with a single strip of varnished cotton to insulate the 
coils. It has ten mercury cups soldered at various distances from 
the center. It must be premised, that in using large batteries with 
this coil, the maximum results by the induced current, are obtained 
by including only a portion of the coil in the direct circuit. With 
small pairs of plates the whole coil should be used. 
A small pair of plates connected with - multiplier, deflects a 
delicate needle at ten feet distance. 
Twelve pairs of plates arranged as an ‘ates series produce 
far more powerful results, than the same elements arranged as a 
calorimotor. The direct current is slightly augmented by passing 
through the coil. When the circuit is broken with a blunt pencil of 
zinc or lead, the spark appears of the size of a large pea, with a very 
loud snap. When both the connexions with the coil are broken 
simultaneously, two equally bright sparks are produced, while a 
third spark occurs in the induced circuit. Fifty pairs of plates give 
no brighter spark than twelve, and three hundred not so bright. 
Charcoal points, in the induced circuit, give a vivid spark, provided 
they do not quite touch. If directly in contact, the action of the 
coil is nearly lost as the current passes directly through the charcoal. 
This shows the reason why the induced current is stronger, when 
half or more of the coil is included in the direct circuit, than when 
the whole is used; in the latter case the lateral circuit is so short, 
that the battery is partly discharged through it. 
It is not impossible that the arch of light may be produced in the 
induced circuit, if the rupture of the direct cireuit could be made- 
commensurate with the velocity of the current. 
To effect decomposition, it is desirable that the circuit should be 
broken with great rapidity. To attain this I have tried a variety of 
means and succeeded in the contrivance of several beautiful pieces 
of apparatus. 
Barlow’s spur wheel answers very well where large batteries are 
used, but not for.small. A stellated wheel, connected by a band 
with a multiplying’ Wheel, answers exceedingly well; but as inde- 
pendence of action is a great beauty and convenience in experiments, 
it must give place to the following self regulating instruments. 
Ritchie’s revolving voltaic-magnet, which has recently come to us 
in connection with Daniell’s and Mullen’s constant batteries, makes 
a good interruptor. Fitted with a glass cell for the mercury, made 
by sections of tubes, it becomes a pleasing and useful apparatus. 
Placed upon the box containing the multiplier, it turns rapidly with- 
