MENTS IN STREET FIRE ALARMS
Year: 1885

page_text: I, JOHN MACINTOSH MACKAY MUNRO, Covepoint House, Gourock North
Britain, Electrician do hereby declare the nature of my invention for IMPROVE-
MENTS IN STREET FIRE ALARMS to be as follows:-
The invention has for its object to improve and simplify the apparatus employed
for Street Fire Alarms.
In my improved system, the battery is at the district central office and the circuit
is normally broken at the street box and there only. When an alarm is to be
given, the circuit is completed by making contact across the break. When the
plunger is pushed in or drawn out or aside a piece of iron which forms the armature
of an electro magnet, drops by its own weight on the pull of a spring into a recess
and through suitable platinum contact pieces, completes the circuit so that the bell
in the district office rings continuously, and, if desired a bell can be so placed in
the street box as to ring also continuously. Although the current now traverses
the E. magnet the armature is far too heavy and distant to be affected by it. The
armature in falling carries with it a little parti-coloured disc so that the colour
shewn at a little view hole in the box is changed at the instant of sending the
message. No matter what is now done to the plunger no further effect is produced
by it. The man on duty at the district office can send a return signal in either of
two ways. He can obviously switch off the current altogether and so leave the
line idle till afterwards adjusted. In this case the sender at the street box would
know that his message was received by his bell ceasing to ring, either all at once
or after prearranged intermittent stops. But preferably, the return signal can be
given by the central office man putting momentarily into circuit a battery large
enough to enable the E. magnet, before alluded to, to draw up its armature sharply
and so break the circuit at the box as at first and replace the original colour of disc
at the view-hole. To make it easy to distinguish between true and false alarms or
replies and also to allow of everything in the box being made strong and heavy
the battery which lifts the armature should be greatly larger than the battery
required to ring the bell or bells,

page_text: A seperate key is provided so that the firemen when at the box or fire can send
signals conveniently to the district office either by working the key or attaching a
telephone or other instrument.
By means of this my invention I do away with the intolerable trouble of having
batteries in the street boxes and that without delicately poised apparatus or slight
variations of resistance as in other systems which are apt to get out of order by the
frequent changes in the condition of "line" and "earth." It also enables the
sender of an alarm to know certainly when his message has been received, and
the receiver to be certain that the alarm has not been given accidentally through
the breaking or the contact of a wire.

page_text: I JOHN MACINTOSH MACKAY MUNRO 136 Bothwell St. Glasgow Electrician do
hereby declare the nature of my invention for IMPROVEMENTS IN STREET FIRE
ALARMS and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
The invention has for its object to improve and simplify the apparatus employed
for street fire alarms.
In my improved system the battery is at the district central office and the circuit
is normally broken at the street box and there only. When an alarm of fire is to
be given the circuit is completed by making contact across this break.
When the plunger p Fig. 8 is pushed in, it displaces a spring catch & which
sustains a weighted bar b, and this bar drops into a recess thus fastening catch a¹
and locking the plunger and at the same time by suitable contact pieces at o
completing the alarm circuit.
(There is also a supplementary contact spring at the end of the plunger so that
good contact is ensured. This extra contact is only used with arrangement as
Plate 1.)
The closed circuit now comprises the battery A Fig. 10 and the alarm bell with
indicator and switch Fig. 9 both at the fire office, and the coils a Fig. 8 in the
street box. There is also in circuit a relay Fig. 10 the object of which will be
hereafter described. The coils a Fig. actuate the armature (not shewn in
drawing) of the bell a.
The intermittent action of the current necessary to work the two trembling bells
Figs. 8 and 9 is secured either by putting short-circuiting contacts on both bells or
by putting the more common make and break contact on the street bell only. This
latter method has the advantage of rendering real and accidental contact alarms
more easily distinguishable as a contact with earth which may occur between the
outer bell and the inner will not produce regular vibrations but simply a single
stroke on the inner bell. It is also worthy of note that, in special circumstances,
a telephone may be used at the fire office to make audible the sounds produced in it
by the street contact, which sounds can easily be made recognizable.
So long as the circuit remains unbroken,-save by the rapid partial breaks
caused by the trembling bells, both bells will continue to ring. The catch s¹ and
plunger being now locked, no errors on the part of the sender of the message can
interfere with its being properly delivered, and it is one of the most distinctive
features of my invention that pressure on the plunger does not hinder the receipt
of reply and that even after the reply is given, the plunger still remains locked so
that the message cannot be repeated to the confusing of its indications or the delay
of the firemen.
The reply is given by the attendant at central office breaking the circuit either
all at once or after prearranged intermittent stops, and he can accomplish the
former in either of two ways.

page_text: He may simply turn his switch 8. Fig. 9 into a so as to disconnect the working
battery A from the line and leave it so disconnected.
Alternatively he may turn his switch s Fig. 9 into c so as to put a much larger
battery B momentarily into line. The powerful current of this battery is able to
break the circuit in the street box by means of the coils a Fig. 8. These coils were
in circuit from the first giving of alarm for they work the armature of the
trembling bell which is of ordinary construction and not shewn in drawing. But
the bar b with its attached armature was too distant and heavy to be lifted by the
current of the working battery from out of the recess into which it dropped when
the plunger was pushed in. When the large battery B is momentarily switched
in, the coils a Fig. 8 become powerful enough to lift the bar b sharply, and so break
the contact which its falling made.
Now it is obvious that, if no provision was made to prevent it, so soon as the
armature bar b was lifted the spring catch 8¹ and the plunger p would be released,
making possible the useless repetition of the alarm, or if the spring catch a¹ was
not released the bar 6 would simply fall down again and restore the contact unless
the large battery was allowed to run itself down through the circuit. The
mechanism must therefore be arranged so as to obviate this. For example the
plunger when pressed could carry before it not only the spring s¹ but a second
spring as 8 which would be placed so as to slip from the plunger so soon as it
passed a certain point; or this second spring could be released by the falling bar b.
83 would then be ready to uphold b when it was lifted, while plunger and 8¹ would
pass over a centre or otherwise fasten themselves. It is needful, however, that the
push required to work the appliance should be as short as possible for many people
will not give a decided or prolonged push, and also that a rapid push should be
effective for some will even use a stone or hammer to strike the plunger. The
apparatus also must not be unstable enough to go off with an accidental shock or
with the breaking of the glass. I prefer, therefore, the arrangement shewn in
Fig. 8. A cross lock is there shewn so arranged that when s¹ is pushed in, the
cross lock is pulled by a spring t so that it fastens down 8¹ in its new position
and at the same time unfastens 82; so that, when the armature bar b is raised,
8 only is free to act. This cross lock is preferably a simple slide as shewn in
drawing.
The armature bar can if desired carry a parti-coloured disc which serves to shew
through a view-hole whether the bar is up or down.
If the simple disconnecting of line from battery A by moving switch 8 into a
with the consequent stopping of the ringing of the bells is relied upon as sufficient
reply, then there need be no armature attached to bar b but it may have only the
ordinary trembling bell armature. The bar 6 with spring s¹ and plunger p then
serve alone as the locking and contact making appliances. The spring 83 with
cross lock (Fig. 8) and the large battery B (Fig. 9) may be omitted. Figures 1
to 6, (Plate 1,) shew the apparatus in this simplified form and are lettered to
correspond with similar parts of Figures 7 to 12.
Fig. 1 shews the design of case adopted in Glasgow and Fig. 2 the method of
distributing the various parts in a manner adapted to the case chosen. The
complete apparatus gives a choice of replies, but, if preferred, either reply can be
relied upon alone and those parts indicated as not needful for that reply may be
omitted, as is done in Figures 1 to 6 where disconnection at the fire office only is
provided for as a reply. The Instruction plate on boxes Fig. 1 reads as follows
Notice. To give an alarm of fire,-break the glass and push the knob firmly―
then wait. The signal will be replied to from the Brigade by the bell ceasing
"
to ring."
. Fig. 10 (or Fig. 6) shews a sensitive relay of ordinary construction which put in
circuit near the battery serves to call attention (through a little local bell and
battery) whenever any of the wires radiating from a station come into contact
with an imperfect earth.

page_text: Fig. 12 (or Fig. 5) is also a similar relay with local bell & but it is not in circuit
with line save when the switch lever at a Fig. 9 (or Fig. 3) is put into a upon
receipt of a fire alarm or contact ring.
Between earth and this relay is a small constant current battery B* strong
enough to hold down the relay but not nearly strong enough to ring the street
bell. This relay has its contacts reversed so that it closes its local circuit not as
usual when pulled down but when let go. Therefore so long as the small constant
current from B' flows in the line the little relay bell does not ring but gives notice
instantly when the line is clear of earth or disconnected by pressure on a Morse
key within the street box. A small switch 811 is provided so that this appliance
may be thrown out when not wanted. But sometimes several alarms or faults are
"
on
at once and it is well that any decrease in their number should be known at
the office.
"
Fig. 11 (or Fig. 4) is a variable resistance. By turning this, adding resistance
till the bell Fig. 12. (or Fig. 5) just begins to ring and then putting it back
one division, the slightest increase in the resistance of any of the faults "on'
immediately allows the bell Fig. 12 (or Fig. 5) to ring again.
"1
Although for greater clearness, five seperate batteries are shown in the drawing
(Plate 2) only two are necessary, viz one large battery B¹ from various parts of
which wires are taken to supply the various instruments and one small battery B*
of two or three cells, giving constant current when wanted. Of course one set of
batteries and relays will serve for any number of alarm circuits.
Two or more street boxes may be joined up to one line but preferably each street
box has its own wire direct to its own bell Fig. 9 (or Fig. 3). A breakage of a line
will not then render useless all the street boxes of a district and as there are no
measurements to take, or resistances to balance before the box which gives the
alarm can be identified, there is no room for mistake and not an instant is lost.
Fig. 8 (or Fig. 2) are terminals suitable for attaching telephones or other
communicating appliances so that firemen can communicate from the scene of a fire
at any time. is a Morse key which is useful for testing purposes and for
signalling to the district station, more especially when the instrument is readjusted
after an alarm.
With the arrangements of Plate 1, the fire office can signal to the scene of fire, if
if they require to do so, by putting working battery A to line thus ringing
street bell.
With the arrangements of Plate 1, the armature attached to b and the large
battery B' may be retained not for reply but for readjustment from office after fire.
Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, I declare that what
I claim is,
b
1. In a street fire alarm box or similar appliance, the combination of a plunger,
pull or lever with a locking bar substantially as described with reference to p
and c Figure 2 so that when plunger, pull or lever is pressed a contact is so made
and the plunger, pull or lever so locked that no interferance with the parts of the
apparatus accessible to the public can break that contact and remake it if broken
by any form of "reply" and hinder the receipt of that reply.
2. In a street fire alarm box or similar appliance an electro-magnet with armature
so arranged that the electro-magnet cannot lift nor hold the armature with the
current used to give alarm but can lift it when a stronger or reversed current is
sent through it.
3. In a street fire alarm box or similar appliance a changing lock which fastens
down a spring or weighted latch displaced by the plunger when an alarm is given
and at the same time sets free another latch ready to act when wanted substantially
as herein before described with referance to p 81 8³ 1 and t Figure 8.
4. In a street alarm or "call" system the connecting of two bells, (or a bell and
a contact-breaker), in one circuit with a contact breaker at one end only, and that

page_text: the end farthest from the battery, for the purpose of distinguishing between a
contact made through the contact breaker and an earth contact not so made.
5. In a fire alarm or "call" system a relay connected substantially as described
with referance to Figures 4 and 5-also Figures 11 and 12-so as to give a signal
when the resistance of one circuit or one of a group of circuits is increased.
6. The use of a switch or key for sending an increased or a reversed current
through an alarm box for the purpose of breaking contact in that box.
7. In a fire alarm system the use of a relay connected substantially as described
with referance to Figures 6 or 10 for the purpose of giving warning when the
leakage of current to line exceeds normal amount.
8. The application of such apparatus as is herein described to Fire Police,
Ambulance or Messenger Call Systems.