ALARM, OR ALARUM, is a term applied to a variety of instruments con structed for the purpose of producing sufficient sound or noise to awaken a person from sleep, or otherwise to give notice of some occurrence, or warning, of the state of the time, &c.
Glenny and Darby's Fire and Burglary Alarm. The object of this invention, for which a patent was taken out in 1820, is to indicate by means of a placard or signal, containing the written information, in what part or situation of the premises to which it is attached, a fire or burglary has taken place, immediately upon either having happened. This is effected by placing an alarm-bell within a box, (having the appearance of any article of furniture,) the internal mechanism of which is connected by lines or wires to every part of the premises deemed to be hazardous. These lines, carried from the alarum in the manner of bell-wires, are at their extremities connected to triggers, any one of which being discharged, releases its line immediately, and sets off the alarm-bell within the box, firing a pistol also, if attached thereto; and at the same time, causes a slider or label to be presented, containing the words, " Fire," or " Thieves," in such a part of the premises, describing where, and which of the two occurrences. The construction of the apparatus is as follows: A box of any external appearance, placed in the bed-room or elsewhere as a piece of furniture, contains the alarm-bell, which is connected to the striking part of a clock. Each of the lines before described, are connected at one end to a piece of metal as a trigger, which is hooked to a hold-fast, placed in such a situation that, by the opening of a door or window, the trigger is liberated, and the line which passes over the pulleys placed at every angle, is drawn back by the other end being attached to a weight inside the box; the weight in descending strikes against a lever formed by a projecting pin, fixed to, and turning on, an hori xontal axis. This axis carries a series of lever pins, corresponding with the number of lines, weights, &c. employed; so that any one of the weights by falling, causes the axis to turn, and by means of an arm projecting from the axis, a wire connected to the striking part is pulled, and the alarm set off. The labels or slides before mentioned are each connected by a line or chain to its respective weight, which, on its descent, projects or draws out to view the label conveying the required information. In adapting this apparatus to indicate the occurrence of itre, small lines of catgut, or threads of sufficient strength, are substituted for the before mentioned lines, which are carried across the ceilings or round the cornices of the apartments to be guarded. Some one of these slender strings, it is considered, would be soon burnt by the ascent of the flame, and give early notice of the destructive element, by the alarm bell to which it was attached being put in action, which would at the same time indicate the situation of the fire. Prior to the granting of this patent, many of the mechanical
arrangements described under it were in use, and the patentee's claim to inven tion may be considered as limited to the introduction of the direction labels, which, in a large building, might prove of eminent use.
Russell's Fire Alarm. This apparatus is put into operation by the expansion of a small quantity of air contained in an instrument called a pulse glass, which consists of two bulbs, with a small tube of communication between them. Into this vessel is put some liquid, usually coloured, so as to about half fill it, the remaining space being occupied by air; it is hermetically sealed. This instru ment is so extremely sensible of a slight increase of temperature, that on placing merely the hand upon one of the bulbs, or gently breathing upon it, the liquid is rapidly forced out through the tube into the other bulb, owing to the expansion of the air within that bulb to which the warmth is applied, and producing an apparent ebullition in the liquid by the bubbling of the air through it. When these bulbs are equipoised upon an axis placed midway between them, it is obvious that the liquid flowing into either bulb will cause it to preponderate ; and to obtain from this preponderating action sufficient force to set off an alarum, Mr. Russell contrived the following arrangement. a represents one of the glass bulbs, nearly filled with the liquid, which should also fill the tube of communi cation up to the opening into the bulb b; the whole of this vessel is enclosed in a cavity cut out of a block of wood, except a portion of a, which is exposed for the purpose of being influenced by an increase of temperature. The block turns freely upon a centre or fulcrum at c, fixed upright in a stand d. e is a long mortised lever or tube, containing four leaden balls, so placed over the fulcrum as to rest in equilibria. Upon heat being applied to the bulb a, the air above the liquid rapidly expands, and drives it into b; the weight being thus increased on that side, causes the lever to descend in the direction of the line f, while at the same instant the leaden balls suddenly roll down the inclined plane, accelerating the descent of the lever, and impart to it a considerable degree of force, which it is evident may be almost indefinitely increased by lengthening the lever, or augmenting the rolling weights. As motion is thus produced, attended with great power, its application to the ringing of a bell, or any number of them, or the firing of a gun, may be easily understood, all that is required being a crank, with a wire connecting it to the alarm used. If a water pipe and stop cock were attached to the fulcrum of the lever, the plug of the latter would thereby be opened, and the floor underneath be deluged with water.