isoith a Description of a Magnetic Contact-hrcaher. 21 



of a single pair by means of this apparatus, a series of in- 

 duced currents may be obtained from the extremities of the 

 longer helix capable not only of communicating a series of 

 intense shocks, but of exerting powerful electrolytic action. 

 This connection is best made in the manner shown in the ac- 

 companying figure, in which R represents a section of the 

 reel, 8 one end of the short helix connected with a cup of 

 mercury in the piece of wood B, Z the other end of the 

 short helix connected with one plate of the battery, whilst 

 the wire C connects the other cup of mercury in B with the 

 other plate of the voltaic couple. It is scarcely necessary to 

 state that the intensity of the induced current may be increased 

 by inserting in the hollow axis of the reel a bar of very soft 

 iron, or what will be still better, a bundle of soft iron wire, which 

 becoming magnetic, will considerably increase the dynamic 

 power of the coil. In this case, indeed, the sparks produced 

 when the ends of the helices round the iron bar E F leave 

 the mercury are very brilliant, accompanied by a loud snap- 

 ping noise and a vivid combustion of the mercury, clouds of 

 the oxide of that metal being copiously evolved. 



If the ends P R of the long and thin coil are furnished with 

 platinum points and immersed in water acidulated with sul- 

 phuric acid, rapid electrolytic action ensues, torrents of minute 

 bubbles of oxygen and hydrogen being evolved. If instead 

 of water the points are pressed upon paper moistened with 

 iodide of potassium, electrolytic action ensues*, iodine and 

 oxide of potassium being separated. Solutions of sulphate of 

 potass and soda, chloride of potassium, sodium, antimony 

 and copper are also rapidly decomposed. In these experi- 

 ments it will be found that the great majority of the electro- 

 positive elements (for example) appear constantly at one ter- 

 mination of the coil, cceteris paribus^ but not all, for it must 

 not be forgotten that on making as well as breaking contact 

 with the electromotor an induced current takes place in the 

 long coil, although of far weaker intensity than the latter, to 

 which it is opposed in direction, and consequently in electro- 

 lytic effects. 



If the ends P R of the long coil are furnished with copper 

 cylinders for handles and then grasped even with the un- 



• If whilst the oscillating bar of the contact-breaker is vibrating rapidly, 

 we fix a piece of well-burnt charcoal on one of the terminations of the fine 

 coil, and draw the other termination lightly over it, a rapid succession of 

 minute but brilliant sparks are obtained. These sparks depend entirely 

 upon the induced current, as the fine coil has no connection with the 

 electromotor. For the exhibition of this, as well as of the electric light 

 of an energetic arrangement, I find pencils of that kind of artificial gra- 

 phite found lining the interior of the iron cylinders used for the distillation 

 of coal in otir gas manufactories very far superior to box-wood, or indeed 

 any other form of charcoal. 



