On Easter Monday last, when several thousands of persons were holiday-making in a public garden out north-westward of London, a loud bang startled the inmates of houses many miles from the spot in all directions--louder than any discharge of artillery, and comparable to a blowing-up on a tremendous scale. It proved on investigation to be due to the explosion of a cylinder no more than twenty-five inches in length by two inches in diameter, filled with one or other of those destructive compositions which chemistry has lately presented to us, and to which have been given the mysterious names of dynamite, lithofracteur, gun-cotton, nitro-glycerine, &c. How such a diabolical sausage got into such a place at such a time, and what the police authorities have had to say about it, we need not detail here; but the subject sets people thinking ugly thoughts about Torpedoes and Infernal Machines. The French have had much to do with (so-called) infernal machines, which, under various forms, have been employed to assassinate successive sovereigns, but happily failed in the wicked attempt, though not without inflicting injuries on onlookers. In 1804, when Napoleon thought that he had England pretty nearly in his grasp, a _catamaran_ expedition was fitted out by the English to act against him. This catamaran was an oblong water-proof box lined with lead; it contained fifteen hundred pounds of gunpowder, various inflammable substances, clockwork to produce an explosion at a given moment, and ballast to steady it. Being towed towards an enemy's ship and left for the tide to float it onward, it would cling to the ship by means of grappling-irons buoyed up with cork; and in a given number of minutes the clockwork acting on a trigger would explode the combustibles. Such at least was the theory; but the chances of failure were found to be too numerous and varied in practice. Some years after this, Colonel Colt, the inventor of the celebrated revolver, devoted a great deal of time to this subject of infernal machines, making many combinations which were useful as hints to later contrivers.