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By Root 16102 0

has been invented by a Mr. Conger of new York, by means of which the existence of fire within a building can be ascertained by a person outside. A small box, containing an air-pump, is placed within the house, in contact with the front wall or door, and from the box, metal tubes, like a gas pipe, communicate with each story of the building. By pulling a knob, such as is usually attached to the wire of a door-bell, the least symptoms of smoke in any part of the building are rendered perceptible. Coincident with this invention is another somewhat similar — that of a self-acting fire-alarm bell. The principle on which it is made is that of the expansion of metals by heat. From a piece of hollow brass, a metal communication leads to a bell, the tongue of which is moved by a spring, not unlike that of an ordinary mouse trap. The fire acts upon the brass, expanding it and causing it to move the apparatus, so as to set the bell ringing. It will strike when the heat is at 120 degrees of Fahrenheit's thermometer, or even at a lower temperature.

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It is well known that when atmospherical air is suddenly rarefied, as wen it issues from the muzzle of an air gun into which it was previously condensed, a fiash [[flash]] of light is perceived, which has been generally attributed to electricity, excited by the sudden expansion. Some interesting experiments on this subject have been made by Mr. Hart, from which he arrives at a different conclusion with regard to the origin of the light.

In his first trials in which he discharged the gun under a variety of circumstances, using dry, damp, and warm air, and discharging it in warm, cold, dry, and moist weather, he failed in procuring light. In these the gun was unloaded; but when loaded, light was instantly perceived; he therefore supposed that it might be occasioned by the friction of the wadding on the sides of the barrel, which induced him to try a variety of substances possessing different electric powers; as dry silk, wool, feathers, shell lac, sugar, and slips of glass. With the first four he occasionally succeeded, but he never failed with the last two, the glass always giving the most vivid light, which was of a greenish color, extending a foot and a half from the muzzle. In repeating some of these experiments, the old silk which had been lying on the floor, and which had become moist and dirty, was again used, and by it a much more brilliant light was emitted than by any of the others; the same was also the case with pieces of split lath, and even with damp saw-dust picked up from the floor. The gun after this was discharged without any wadding in the barrel, when it always gave light at the first shot after the magazine was charged. From this it was suspected that as its muzzle rested against a wall during the charging, some sand or lime might have fallen in, the attrition of which during the discharge may have caused the luminousness. Accordingly, on taking precautions against this, no light could be obtained, which induced Mr. Hart to introduce a little sand, by which a beautiful stream of light was produced at each discharge. From these experiments, it is evident that the effects were occasioned by attrition, and that the sand adhering to the old wadding, saw-dust, split lath, etc., was the cause of the light; hence on trying these when quite clean none was observed. To ascertain whether the light from these was produced by the abrasion of particles of iron from the inside of the barrel, like sparks from a cutler's wheel — sand, fragments of spar and sugar, were held at the muzzle of the gun when discharged, by which they appeared slightly luminous. When a grating composed of clean and dry thermometer tubes was held in the same situation, there was no light — proving that the luminousness is not occasioned by any electrical appearance excited by the air striking against the objects: we must therefore consider it as caused not by any change which the condensed air undergoes, but merely by attrition, and therefore similar to what occurs in common cases of friction.