Electric Bells and All About Them

breaking the circuit between the bell or bells, on the one hand, and the battery on the other. This necessary piece of apparatus, which is simply a contact maker, receives different names,

and one of which is connected with one of the wires from the battery, while the other is attached to the wire proceeding to the bell. When the button is pressed the upper spring comes into contact with the lower metal spring or plate. The circuit is now complete; hence the bell rings. But as soon as the finger is removed from the stud or button of the "push," the spring returns to its old place, contact being thereby broken when the b

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interior arrangement is precisely similar to that of the push; that is to say, the pressel consists in a pear-shaped or acorn-shaped hollow wooden box, with a projecting knob or button below. This button is attached to a spring, the tension of which keeps the knob protruding from the end of the

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uit is completed. Closely allied to the "pull" is a form of bedroom contact, which combines pear-push or pressel and pull in one device. This will be readily understood on reference to Fig. 48. Another form of bedroom pull, with ordinary rope and tassel, consists in a box containing a jointed metal lever, standing over a stud, from which it is kept out of contact by a counter spring. To the projecting end of the lever is attached the bell rope. When this is p

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Fig. 43 A. That is to say, an electro-magnet wound with wire, and surmounted by a thin iron disc, is placed in circuit with the line wires. The ringing of the bell rapidly magnetises and demagnetises the el

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be directed, is that known as the burglar alarm, with its v

hardened brass or steel insulated from the plate; or of a cylindrical box with a spiral spring inside (see Fig. 51). It is so arranged that as long as the stud is kept pressed in, the platinum points of contact are kept apart; this is the position when fixed in the rebate of a closed door or window;

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ttaching it to a hook or button. A slight pressure against the blind (caused by anyone trying t

h a rubbing action (which tends to clean the surfaces and then make a good contact) is brought into play, rather than a merely dotting action. For this reason, spring contacts in which the springs connected with the wires are kept apart by an insulating wedge (shown at Fig. 53) as long as the door or window are kept closed, are preferred. In the case of windows, strips of brass let into the frame on each side of the sash, are thrown into contact by the springs a and a

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cian (and alas! to what base uses may not even science be perverted) he will begin by cutting all suspicious-looking wires before he attempts to set about any serious work. This disadvantage may be entirely overcome by the adoption of a simple modification, known as the "closed circuit system" of bell ringi

s great expense; besides which one can never be sure that the contacts and wires are in proper order without actually trying each one. On the other hand, with the "closed circuit" system, one has merely to place the wire in any convenient position, it being better seen than hidden. The very fact that alarm is given on breaking the contact renders the method applicable in circumstances and under conditions which would render the "open" method difficult and expensive, if not impossible. One c

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s. Consequently the armature is drawn away from the contact stud, close up to the electro-magnet, and is held so. When a break occurs, the armature fli

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the surface of which is pierced with holes. This stands immersed in dilute sulphuric acid. A saturated solution of copper sulphate is next carefully introduced, so as to displace the acid upwards. Crystals of sulphate of copper are introduced into the open end at the top of cylinder, to fill the perforated portion at the bottom. From the wooden cover of cell a thick flat ring of amalgama

ial contacts, which break contact when the pressure is removed, must be em

50, 53 and 54, may be fi

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delicacy, it has the advantage of being able to give notice of low, as well as of abnormally high temperature. The form usually given to the electric alarm thermometer, is well shown at Fig. 59. It consists in an ordinary thermometer with a wire projecting into the tube to a certain point, say 100 degrees. The mercury in the bulb being al

e, as well as a rise beyond a certain fixed point. These thermometers are specially used by nurserymen and ot

to the right if heated, and to the left if cooled. In the instrument shown at Fig. 60, the application of heat causes the flexible strip carrying the contact screw, to bend over till it touches the lower s

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he aneroid barometers. When the temperature rises to a certain point, the expansion of the air in the chamber brings the metallic plate into contact with the screw, as shown below. This closes the circui

their action upon some arrangement whereby when the hour hand of the clock or watch arrives at a certain given point in its travel, it makes contact between the battery and bell. In general the contact piece is attached bodily to the clock, but in the ve

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ds the number of places the watchman in charge has visited or missed on his rounds. This

s as there are places to be visited by the watchman-any number from one to twenty. Each division has a corresponding marker, which indicates, by the impression it makes upon the paper, the time the watchman visits the place connected with that marker. Wires are carried from the terminals of the clock, one to the battery, and one to each press-button fixed at the points intended to be visited by the watchman; another wire

ent, who can thus, from time to time, satisfy himself of the watchman's vigilance.

jesty's Commissioners in Lunacy, and has been adop

cal battery of greater power to be used for actuating the markers. This has made no alteration in the

t when the water rises to the level of the float and lifts it, it causes the contact piece to complete the circuit through a set screw. Or the float may be attached to an arm having a certain play in both directions, i.e., up and down, wi

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screw is fixed to each brass plate, to connect up to the leading wires. When the plug is in its socket, the circuit between the two plates (and consequently between the battery and bell, etc.) is complete; when the plug is out, the contact is broken. This form of switch is subject to work out of order, owing to the fact that the taper plug gradually widens the hole, so that the contact becomes uncertain or defective altogether. By far the better form of switch is the lever switch, as shown at Fig. 64. This consists in a movable metal lever or arm, which is held by a strong spring in contact with the upper binding screw. It can be made to slide over to the right or le

ontact with the stud in the front of the base-board. As both the stud and the lever are connected to binding screws communicating with the battery and bell, etc., it is evident that on depressing the key the circuit with the bell will be completed for a longer or shorter period, varying with the duration of the depression. Hence, either by using preconcerted signals of short and long rings to sig

educe bell signals to a definite system, and use this system or code as a means to carry on conversation at a distance as intelligently as it can be done by a pair of telegraph instruments. In fact, the Morse telegraph code can be ea

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e represented by five strokes of varying length to each figure. Stops, and other marks of punctuation, are represented

y A A A or

.) " I I I

n (?) " U D

" B A " -

(') " W G "

as (") " A F

( ) " K K

(;) " K Ch

) " N Ch "

" I Ch " –

arry on a conversation in this way it is necessary to be as punctilious in time as when playing a piece of music on a piano, if the signals are to be understood. The dots of the signal should therefore be represented in time by one, and the dashes by two, whilst the spaces betwe

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2 3 2 1

R I

- – – - – –

2 1 1 2 1 1

A

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1 2 2 1

achman

A

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1 2 2 1

tress is read

N G

– – - – - -

1 1 2 1 2 2 1

R I

- – – - – –

2 1 1 2 1 1

stood, or the double short signal I – – when the word is not understood. A negative reply to a question may be given by the signal for N - –, and an affirmative by the signal for ? – - – -; other abbreviations may be devised and used where desired. The code having been committed to memory, it will be qui

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y turning the screws B or C. These two screws are both borne by a double bent arm (of metal) affixed to the pillar D. This pillar is separated from the rest of the frame by an insulating collar or washer of ebonite, so that no current can pass from E to D, unless the armature be pulled down so as to make contact with the contact screw B. Just under the armature, stands the electro-magnet G, which when energised can and does pull down the armature A. It will be readily understood that if we connect the wires from the electro-magnet G, to the wires proceeding from the battery and push (or other form of contact) at the distant station, the electro-magnet, being wound with a large quantity of fine wire, will become sufficiently magnetized to pull the armature down through the small space intervening between C and B; so that if the screws D and E are connected respectively to the free terminals of a battery and bell coupled together at the nearer station, this second battery will be thrown into circuit with the bell, and cause it to ring as well and as exactly as if the most skilful and most trustworthy assistant were in communication with the distant signaller. Every tap, every release of the contact,

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icator," we have a most ingenious application of the same principle in a very compact form. In this (Fig. 68), the electro-magnet is placed directly behind a disc-shaped iron armature, on which is painted or marked the number of the room etc. (in this case 4); this armature is attached by a springy shank to the drop bar, shown to the left of the electro-magnet. In front of the armature is a light metal disc, also pivoted on the drop bar. This engages in a catch above, when pushed up so as to cover the number. When pushed up, the spring of the armature retains it in its place so that the number is hidden. When the current passes around the electro-magnet, the armature is pulled toward it, and thus frees the covering disc, which therefore falls, and displays the number. The ordinary form of "fall back" indicator (a misnomer, by the way, since the indicator falls forwards) is well illustrated at Fig 69. Here we have an ordinary electro-magnet A, with its wires w w' standing over an armature B attached to a spring C, which bears on its lower extremity, a toothed projection which serves to hold up the short arm of the bent lever D, which supports the number plate E. When the electro-magnet A is energised by the current, it pulls up the armature B, which releases the detent D from the tooth C; the number plate therefore falls forwards, as shown by the dotted lines, and shows itself at the aperture E′, which is in front of the indicator frame. To replace the number out of sight, the attendant pushes back the plate E, till it again engages the bent lever D in the tooth C. This replacement of the number plate, which the attendant in charge is obliged to perform,

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dicator frame. Stops are usually placed on each side of the pendulum rod to limit the swing. When the electro-magnet is magnetised by the passage of the current, the armature is pulled suddenly on one side, and then the pendulum swings backwards and forwards in front of the aperture for some minutes before it comes to rest. When fitted with silver fluted glass, the motion of the vane is clearly visible even in badly lighted places. As the pendulum, after performing

e V opening, a brass stem carrying the signal card is screwed into the armature, the action being, that when a current is allowed to pass through the electro-magnet the armature with the pendulum is drawn towards it and held there until the current ceases to pass, when it instantly looses its hold of the armature, which swings away and continues to oscillate for two or three minutes, so that if the servant happens to be out of the way, it may be seen on her return which pendulum has been set in motion. The Pendulum Indicator we have recently patented is entirely self-contained.

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by means of a relay (fixed in the same frame) and a local battery. This is shown in Fig. 71, where a second pair of wires attached to C and C, to the extreme right of the indicator frame, are brought from the same battery to work the indicator and contained relay. It is not advisab

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ach side like a V, forming, as it were, three poles. Though but one bobbin is used, the effect is very powerful. There are no springs or other complications, so that the arrangement is adapted for ship use, as are also those represented at Figs. 67 and 68. Pendulum and fall-back indic