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 this multiplier, deflects a 

 delicate needle at ten feet distance. 



Twelve pairs of plates arranged as an alternating 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 df 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 circuit 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 interrupter. 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- 



