MECHANICS AND USEFUL ARTS. 83 



by the employment of frictional in the place of voltaic electricity. A 

 very portable arrangement of a plate-electric machine, with Leyden 

 jars and the other necessary implements, and with a small stove at- 

 tached to protect the apparatus from the prejudicial interference of 

 damp, has been employed with success in some extensive operations in 

 that country, as many as one hundred charges having been simul- 

 taneously fired by its means. 



Some results obtained in connection with Professor Wheatstone, in 

 prosecuting an experimental inquiry into the merits of the different 

 forms of electricity in their special application to the explosion of 

 mines, are worthy of notice : Our attention being particularly di- 

 rected to the application of the electricity obtained by induction from 

 permanent magnets, it was found that, although gunpowder could 

 be ignited by the magneto-electric spark, the explosion of a single 

 charge, by the use even of one of the most powerful magneto-electric 

 machines, could not be relied upon with any degree of certainty. By 

 employing, as a priming material, a gunpowder slightly modified in its 

 composition so as to increase its conducting power, the ignition of one 

 charge, but of one only, was effected with certainty. After trying 

 with no better success a large number of explosive compositions of a 

 more sensitive character than gunpowder, I at length lighted upon a 

 material which combined the properties evidently essential to the suc- 

 cessful employment of the magnet, namely, considerable sensitiveness 

 as an explosive and moderate power of conducting the current. By 

 its employment as the priming material, in connection with an appro- 

 priate fuse arrangement for the purpose of permanently fixing it in a 

 position most favorable to the proper action of the current, it was no 

 longer necessary to employ a powerful magnet to effect with certainty 

 the explosion of single charges. Here is a small electro-magnetic 

 machine of comparatively low power, of the kind and size employed 

 by Mr. Wheatstone in his smallest portable magneto-electric telegraph 

 instruments. I have connected with it, by means of these two long 

 wires, two small charges of powder, each containing the primed 

 fuse just referred to. You will perceive that as soon as the action of 

 the instrument is established by setting in very rapid motion this little 

 arrangement of multiplying wheels in connection with the movable 

 armature, the charges are exploded. Advantage is taken of the very 

 rapid succession of currents obtained from such an instrument as 

 this, or, better still, of an arrangement of several such electro-mag- 

 nets, to effect the ignition of a considerable succession of charges 

 with such great rapidity, that the result is practically the same as 

 though the explosion of the whole number occurred instantaneously. 

 A portable combination of several of these little instruments^ such as 

 has readily been devised by Mr. Wheatstone, and is contained in this 

 small box, is all that is, therefore , required, in addition to fuses and 

 connecting wires, for exploding, at the shortest notice, a considerable 

 number of mines. The advantages offered by the use of such an ap- 

 paratus are very important. With the most ordinary care it is not 

 liable to injury or disarrangement ; it is exceedingly transportable and 

 ready for use at any moment, and the soldier requires but very little 

 instruction in its employment. He has only to place the instrument in 



