AN IMPROVED THERMO-ELECTRIC ALARUM
Year: 1869

page_text: PROVISIONAL SPECIFICATION left by Alexis Lacanau at the Office
of the Commissioners of Patents, with his Petition, on the 18th
September 1869.
I, ALEXIS LACANAU, of Grasse, France, Gentleman, do hereby declare
the nature of the said Invention for "AN IMPROVED THERMO-ELECTRIC
ALARUM," to be as follows:-
The Invention relates to an improved thermo-electric alarum for
lighthouses, signal lights on railroads, drying stoves, rooms of houses or
other dwellings, museums, or other similar places where certain fixed
degrees of heat are to be kept up, and so that the alarum by sounding &
bell or other similar means is to call the attention whenever the heat
should in lighthouses or signal lights, for instance, fall below a certain
degree in consequence of the diminution of the light and of the heat
evolved by this latter, or in drying stoves, dwellings, or other similar
places, in consequence of a fire breaking out or other contingencies,
rise above a certain fixed standard. For this purpose I use the apparatus

page_text: of the annexed Drawing, and which consists of a helical or other
suitable compensating spring L, which becoming distended by an
increase and contracted by a diminution of the heat acts in those cases
(according to, if desired, a decrease or an increase of heat is to be
signalled) for establishing an electric circuit which causes an alarum to
be sounded in a manner analagous as is done for such apparatus in
electric telegraphs, whilst as long as the fixed normal degree is kept
up the spring keeps the electric circuit broken so as not to effect the
alarum.
The apparatus may be constructed as follows:-P is a disc of copper
or other suitable metal provided with two studs E and E¹ and binding
screws K and K. The stud E is kept isolated from the disc P by a
washer C of ivory or other suitable isolating material, and to this stud E
is connected the positive wire F of a galvanic battery situated at a
railway station or other suitable place. The negative or earth wire F
of the battery is connected to the other stud E', which latter is in
metallic contact with the disc P. This disc carries another disc D of
copper or other suitable metal, which disc may be caused to turn on a
pivot M. by means of a handle g, the lower end of which may be inserted
in one of the holes h for allowing to vary at pleasure the position of
the free end A' of a compensating helical spring L, the other end A
of which is fixed to the pivot M, and which spring is formed of 3 strips
of metal soldered together, viz., one of platinum, one of gold, and one
of silver. B, B', is a lever turning on a pivot O; when this lever
by the effect of the end A' of the spring L is carried in the position
shown in dotted lines the electric circuit is broken. This is the normal
position, whereas when by an increase of heat the spring L extends itself
and presses no further on the arm B of the lever B, B¹, a spring R
carries the opposite arm B' in contact with the stud E, and thereby
establishes the electric circuit which carries at once an alarum into
operation in the manner similar that takes place for alarums of electric
telegraphs. If consequently in a lighthouse provided with this apparatus
the lights are in due order, the heat evolved by them keeps the spring
L extended, and causing thereby its free end A¹ to press on the arm B
keeps the lever B, B', in the position shown by the dotted lines,
whereas when the lights or part of them should become extinguished

page_text: the end A¹ of the spring L recedes, and pressing no longer on the arm B¹
of the lever B, B¹, the other arm B' of this lever will touch the stud E,
and thus establishing the electric circuit carries the alarum into operation,
which will at once call attention. A contrary disposition in respect to
the mode of acting of the spring L might be adopted.