Magnetic Galvanism. 81 



Spa7'ks. — These always occur between the keeper and magnet or 

 between the wires c and e when they are brought close enough to 

 each other, but if the latter touch, no sparks can be produced be- 

 tween the keeper and magnet as in this case, a continuous metallic 

 circuit exists by means of the coil and the wires. Gold and silver 

 foils, placed between the keeper and magnet or hung loosely be- 

 tween the wires c and e, exhibit their characteristically colored light, 

 and tinder may be ignited by holding it beneath the magnet when the 

 keeper is passing off. The color of the sparks, is variable, sometimes 

 brilliant white and at others copper red. The number, magnitude 

 and brilliancy of the sparks, are exceedingly increased by this ar- 

 rangement of the instrument. Upon several occasions, owing, ap- 

 parently, to the combustion of shreds from the keeper, I have produ- 

 ced sparks nearly an inch long. No loud snap or noise accompa- 

 nies them and it seems probable therefore, that they are purely gal- 

 vanic, yet when the metallic foils are placed between the magnet and 

 keeper and the latter pulled off, an indistinct crackling noise may, al- 

 most always, be heard. 



The brilliancy of the light between the magnet and keeper, will 

 be always greater, by preventing these parts from communicating at 

 any other surfaces than those of the poles. The brass plates, in par- 

 ticular, should be varnished, or covered with silk on the outside, 

 whenever, from the narrowness of the magnet and the quantity of 

 included coil, the chances of contact become frequent. The follow- 

 ing simple expedient, will enable the galvanic light to become appa- 

 rent to a class. Place a piece of very fine wire, (such, for example, 

 as the wire upon the finest guitar string,) so as to lie upon the upper 

 part of the keeper and at the same time, press against the face of 

 the magnet, secure its contact by the thumb and draw down the 

 keeper swiftly. The end of the wire, being the last part in contact 

 with the magnet, will give out a brush of brilliant sparks, closely re- 

 sembling those obtained by rubbing together the conducting wires of 

 an active battery. If for the elastic wire, we substitute metallic foils, 

 and arrange them similarly, the sparks will be very brilliant and ex- 

 hibit the characteristic colors. 



Shock. — This may be felt in the fingers, by touching the magnet 

 with the left hand and sliding the keeper off with the other ; it is al- 

 most always perceived in the fingers resting on the magnet. The 

 wires c and e must, of course, be kept apart. The most disagreea- 

 ble and sudden shocks, are experienced by putting these wires into 



Vol. XXIV.— No. 1. 11 



