To construct an apparatus that will, under every condition of atmosphere, whether damp, dense or rarefied, evolve, at the will of the operator, abundance of electricity; such electricity to possess the property of developing intense heat, so as not to need a very sensitive priming, and to possess sufficient tension to overleap numerous solutions of continuity, say fifty, at a flash. Next, to discover a priming composition, to insert between the solutions of continuity, that would not be affected by moisture, that would bear handling without danger of exploding, be unchangeable for years, unaffected by the induced electricity of the atmosphere, whether caused by thunder storms, lightning on the rail, machinery belting in motion, or steam blowing off from a safety valve, ozone, etc., and yet not too exhaustive of the electric force of the spark required to fire it. The above seemed to me the conditions necessary for the apparatus and the exploder in firing with electricity. In addition to these, for conducting such electricity to the points required, the best conductor, and the best insulation attainable. Further, that as Nitro-Glycerin was an expensive explosive to waste, to supplement the above details with some material that would absolutely develope its extreme force instantaneously, and not as is easily the case, burn a part, explode a part, and throw the remainder into the atmosphere, to poison the miners, or by missing fire, endanger life, and waste time. How these objects, so desirable, have been obtained, I now proceed to relate. By modifying the ordinary induction coil, so as to make it yield a highly heating spark, and remedying its property of losing tension rapidly after leaping four or five solutions of continuity, the Messrs. Ritchie & Sons, of Boston, have constructed for me a coil that fires 18 intervals when charged with rifle powder simply; and they are now constructing another coil capable of firing fifty mines, when charged with priming that is perfectly safe to handle, and fulfilling the conditions enumerated above. One spark alone is required to effect these results, which may be summed up as “eliminating the heating properties of induced electricity.”