A few weeks ago we corrected the reports which had been disseminated by many of our daily papers in regard to the novelty and utility of an explosive gap, engine which had recently been exhibited in Paris. We stated that an engine, similar in every respect, had been invented long ago by Dr. Drake, of Philadelphia, and was exhibited during two fairs of the American Institute in this city, and finally destroyed by the burning of the Crystal Palace. Although we have done all this, we notice that our cotemporaries are still using their columns in describing the exploits of the Paris gas engine. Explosive gas and explosive powder engines are juite old. Twelve years ago, when gun cotton was first prominently introduced, quite a number of enthusiastic inventors believed that it might be employed as a substitute for steam, and theoretically various advantages may be claimed for a solid and suddenly expansive agent like gunpowder or gun cotton. Thus, with a package of gun cotton and a small galvanic battery, a portable explosive engine maybe transported from place to place and operated on mountains or plains, for purposes of peace or purposes of war, for which it would be a most terribly efficient and destructive agent. The gas engine requires that coal be made into gas before it can be operated, and in this respect it is far more complex, troublesome and expensive than the steam engine. The gun cotton engine would require neither boiler nor furnace like steam and hot air engines, but it will be yery difficult to give it an equable motion because the expansion of the charges is so ssdden that they tend to produce great irregularity of motion in the piston. On page 180 Vol. III. (old series) of the SCIENTIFIC AMERICAN, we illustrated a gun cotton engine, invented by the celebrated W. Fox Talbot, of England inventor of the Talbottypethe charges of which were ignited by electric sparks, like the gas engine in Paris. It never came into use; it merely reached the condition of an experiment, but some other inventor may yet be able to improve upon the first ideas, and render such an engine useful for many purposes.