sight, or limb. Such being the object for which I first 

 contrived an apparatus for this employment of electricity, 

 I am sure you will join me with equal ardour in spreading a 

 knowledge of the process, and in inducing workmen and 

 masters to use this safe and powerful agent in their daily 

 operations in mines and quarries. Were this object too 

 feeble an incentive, (which I would not for a moment believe 

 it to be in this Christian and charitable country,) I might 

 perhaps arouse masters to a sense of its importance, by 

 showing them how great would be their gain in a pecuniary 

 point of view, for it can be proved that at least one-half the 

 gunpowder necessary in the old process would be saved by 

 the adoption of this new method ; indeed, a correspondent 

 in the Mechanics' Magazine, who states himself to be con- 

 nected either as lessee or proprietor of slate mines in North 

 Wales, says, that he finds one pound of gunpowder as 

 eflPective, by the use of the several precautions I have pointed 

 out, as ten pounds, if used on the old plan of blasting rocks. 

 To explain more easily in what manner the freedom from 

 danger is obtained, it will be well that I first describe the old 

 method of blasting, together with the dangers attendant on 

 it, especially as there may be many now present not con- 

 versant with the operation. When a rock is to be riven or 

 torn from its bed by gunpowder, a hole is bored in the 

 necessary position, about two inches in diameter, and varying 

 from two to twenty feet in depth ; when dry and clean, the 

 charge of powder is poured into it, and in order that the 

 force of the explosion may as much as possible be expended 

 upon the rock, the charge is confined in this hole by filling it 

 with loose stones or gravel, (technically called tamping or 

 stemming) from the gunpowder to the surface of the rock, 

 with this exception, that a small aperture or channel is 

 allowed to remain through the tamping stuff", for the purpose 

 of firing the charge of powder, by a match or train, from 



