Lastly, it is found that Nitro-Glycerin when exploded by a charge of mercuric fulminate, will not bring about the explosion of compressed gun-cotton placed in contact with it, though under precisely similar circumstances the explosion of gun-cotton or of Nitro-Glycerin will induce the explosion of a larger mass of its own kind. These results point to the conclusion, that the effect of the detonation of one substance in causing the explosion of another depends not only on the force, but also on the nature of the vibrations developed in the former; the most probable explanation of the observed results being that the vibrations attendant upon a particular explosion, if synchronous with those which would result from the explosion of a neighbouring substance in a state of high chemical tension, will, by their tendency to develop those vibrations, either determine the explosion, or, at least, greatly aid the disturbing effect of mechanical force suddenly applied, while, in the instance of another explosion, which develops vibratory impulses of a different character, the mechanical force applied through its agency, has to operate with little or no aid, so that greater force or a more powerful detonation is required in the latter case to accomplish the same result. D. NITRO-GLYCERIN CAR OFF THE TRACK. The perfect safety with which Nitro-Glycerin can be transported, when congealed, is demonstrated in the following fact, which should effectually banish from the minds of freight agents and express companies the objections which they have heretofore successfully urged against carrying Nitro-Glycerin by rail; so far, at least, as concerns that manufactured by the writer. On May 3, 1872, a special car loaded with seventy-nine cans containing 4,800 pounds of congealed Nitro-Glycerin, was being transported over the Chesapeake and Ohio Railroad, from Huntington to Charlestown; C. J. Cheshire, Assisting-Superintendent at the Maysville, Ky., Works, was on the car running at the rate of 18 miles an hour; suddenly the car jumped the track, and was dragged over the ties, some of which were two feet ten inches measured distance apart (the new roadway not then ballasted), for a distance of 684 feet, before the train could be brought to a stand still, to the no small consternation of Mr. Cheshire, the engine-driver and stoker. The rough jolting had no effect whatever on the Nitro-Glycerin, except tumbling some of the cans off the car, and in a few hours, the car being replaced, transportation was resumed, and one more experience of the properties of our Nitro-Glycerin added to the list. E. ACCIDENTS AT THE HOOSAC TUNNEL.