ALARUM. It is curious to mark how much ingenuity has been displayed within the last few years in the invention of alarums, and how many patents have been taken out for the inventions. In all such contrivances there is some little bit of mechanism or other which gives a shrill sound whenever atten tion is required to be directed to any subject with which the alarnm is associated.
Without describing any of the older forms, we may glance at a few of the modern sug gestions. A Mr. Allen, in 181t, registered an alarum intended to prevent injury to boilers from the water falling below its proper level. The machine consists of a float within the boiler, a steam-whistle on the exterior, and a tube of connection. When the water is at a proper height in the boiler, the float is buoyed up, and the whistle is silent ; but when the water, and with it the float, descends too low, a little valve in the tube opens, and a current of steam from the boiler ascends to the whistle, which immediately gives forth a shrill sound, thereby indicating that the Water has sunk too low in the boiler.
The alarums suggested within a recent period for use on railways, are exceedingly numerous. One patented by Mr. Doull, is a railway whistle, so constructed as to yield several notes, capable of being combined into a code of signals. A chemical alarum by Mr. Mowbray consists of a copper cylinder, with a whistle at the top. A piece of car bonate of lime and a little muriatic acid are put into the cylinder, by which carbonic acid gas is speedily generated ; and this is forced by some kind of mechanism into the whistle, whenever a sound is required to be produced. A contrivance by Mr. Hoare, described before the Society of Arts, consists of a chain of rods extending from end to end of a railway train, and moving freely on joints. At the end of the chain, in the guard's carriage, is a crank which, when the rods rotate on their axes, comes in contact with a hammer, and causes it to strike a bell. The driver, or the pas. sengers in any carriage, can give a slight rotatory motion to the rods, and thus signals be communicated.
But the busiest contriver of alarums, per haps, is Mr. Rutter, who has called to his aid the marvels of electricity. In a patent for several such contrivances, taken out by him in 1817, one variety is the Fire Alarm, a complicated apparatus intended for use in large buildings. &galvanic battery is placed in one room, the alarum in another, thermo meters in every room, and copper wires to connect all these pieces of apparatus. If the temperature of any room be greatly raised, as by accidental fire, the rising mercury in the thermometer comes in contact with a metallic wire, which sets the galvanic battery in action, and this again works the alarnm bell in the same way as an electro-telegraphic clock, but with an adjustment intended to show in which room the rise of temperature has occurred. A second variety, the Trespass
Alarum, depends for its action on the placing, near every door and window, of a tube con taining mercury, open at the top; the open ing or closing of the door or window brings a small wire into contact with the surface of the mercury, and this completes a galvanic connection with a battery in another room: all the parts of the apparatus may be the same as those in the fire alarsuu, except by having open tubes of mercury near doors and windows, instead of thermometers in each room. A third variety, the Railway Alarum, is intended to establish signals of communi cation between the guard and the engine driver of a railway train. There is a copper wire carried through or upon or beneath each carriage, and connected with another in the adjoining carriage by a flexible metallic cord: the wire and cord being coated with gotta percha to secure isolation. There is thus a wire-communication from end to end of the train. The guard has in his box or seat a very small galvanic battery; and the engine-driver has a series of small studs connected with the rail on which his hand is usually resting. When the guard wishes to communicate with the engine driver, he sends a slight galvanic shock through the wire to the spot on which the hand of the driver rests ; and the duplica tion or variation of the shock maybe made to indicate various signals.—It must be evident that great completeness and exactness would be necessary to render any of the above three kinds of alarum efficient for the purpose in tended.
A floating alarnm was suggested a few years ago by Mr. Hobbs, of Bristol, to be moored to a sunken rock or other dangerous place at sea. The centre of the machine is an air-vessel or buoy. At each end is a box in which a whistle is fixed, whose month is protected from the water. As the water of the sea circnlates in certain parts of the in terior of the machine, it drives the air alter nately from one end to the other, and impels it through the whistles; and the more vio lently the sea rocks the floating machine, the louder will the whistles give forth their sound. The proposal of the inventor is to make the buoy and whistles of such dimensions that the sound may be heard some miles distant.
Many of the above good things remain in the form of mere suggestions, not yet practi cally carried out; and it must be owned that some of them are rather cumbrous and com plicated.