An Improved Electrical Safety Lamp for Miners.
Year: 1898

page_text: Date of Application, 8th Mar., 1898-Accepted, 16th Apr., 1898
[Communicated from abroad by OTTO SIEDENTOPF, of No. 131, Leipzigerstrasse, Berlin,
in the Empire of Germany, Engineer.]
An Improved Electrical Safety Lamp for Miners.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
All the attempts which have hitherto been made with the view of introducing
electrical safety lamps into practical use in the mining industry have been
frustrated more or less completely by the brevity of the "life" (or duration of
illuminative effect) of the lamps in question, being incandescent lamps. The reason
why those lamps are comparatively short-lived is that their incandescent filaments, in
order to be absolutely proof against any danger of explosion, must be charged with
current not exceeding a pre-determined amount (density or amperage), while on the
other hand it is upon this amount of current that the strength and resisting force of
the filament is dependent; this resisting force being at the same time influenced by
the pressure of the current (or E M F)-which in the lamps referred to is limited-
and also by the decline in the voltage occurring in the process of discharging the
accumulator connected with the lamps. By way of example, the average life of an
incandescent lamp of that class, of three candles normal illuminating power, may be
said to attain 100 hours at the outside; so that, laying down the length of each
work-day at eight hours, and allowing one hour for rolling the wagons in and out and like
accessory operations, such a lamp may be expected to last approximately 11 days.
Assuming, then, that 1000 lamps of this description are regularly in use, the light of
100 of those lamps will in consequence go out daily during working hours, and as
many fresh lamps should be provided to supply the deficiency. This, however-even
leaving the added cost of having spare lamps in readiness for such an emergency
out of account.-is in most cases, occurring in actual practice, found to be an
impossibility.
According to the present invention it is proposed to remedy the drawback stated
by providing the miner's lamp with two or more illuminant bodies supplied with
current from the same accumulator or storage-battery; one of such bodies, being
designed to serve as the main light and the other as a reserve or emergency light.
The life of a safety lamp thus fitted with two light-emitting bodies, may be determined
by computation as follows:-One main light goes out, on an average, every eleventh
day, when the reserve light must come into operation. On that (the eleventh) day
it will have to "turn," let us say, for an average space of five hours. When the work-
day is over, the main light is provided by the attendant with a fresh globe or bulb
and, in each case, at the beginning of the next work day, is connected to the
battery as a "main" light. Seeing, therefore, that each reserve light only comes
to be used every eleventh day, and even then only for half the time of normal
operation of the main light, such reserve light will illuminate 22 times as long as the
main light; with the result that the average life of such a lamp, provided with two

page_text: illuminant bodies, will-in the hands of the miner-be 11 × 22-242 days; while,
as a matter of course, the provision of any spare lamps is thereby rendered altogether
superfluous.
Besides, the arrangement of the improved safety lamp, forming the subject of this
invention, is such, that the lamp cannot be opened during working hours, whilst under-
ground. Accordingly, it is not in any gallery or part of the mine that the bulb is
renewed; in fact the miner using the lamp is to be precluded from ever attempting
arbitrarily to connect or disconnect the same. What will happen in practice is
this :—The lamp, with the main light "burning," will be handed to the miner who,
subsequently, by means of a switch specially devised for the purpose, need only
connect the reserve light to the current supply when this becomes necessary; but
having once done this, he will be able to make no further connection, either back
wards or forwards; owing to which provisions it may at any time be readily
ascertained whether or not any abuse in the handling of the reserve light has been
attempted.
The safety lamp may be provided with two illuminant bodies for example, in various
ways, viz. :
(1) The incandescent lamp may be fitted with two filaments independent of each
other each of which may be switched into a separate circuit. The disadvantage of
this arrangement is, however, that the bulb, after the extinction of the main filament,
only retains the reserve filament, so that it becomes unfit for further use for any
length of time, and has to be exchanged at the completion of the work-day; or
(2) Under a protecting glass two bulbs may be fitted with separate holders; an
arrangement which, while it possesses the characteristic of great simplicity, is
attended with the defect that the rays of light from one incandescent lamp are
interfered with by the body of the other; or again
(3) The safety lamp receives two illuminant bodies located apart from each other,
each being placed under a separate protecting glass and controlled by a separate
switch or one common switch may serve to operate both.
The form of lamp represented by way of example in the accompanying drawings is
supposed to be carried out in accordance with paragraph 3.
In the said drawings,
Figure 1 is a front elevation of the improved safety lamp;
Figure 2 is a sectional side elevation of the same with the lid closed;
Figure 3 is a side elevation of the open lamp; and
Figure 4 is a diagram illustrating the manner in which the two illuminant bodies
are connected.
a is the main lamp which is protected from external influences by a protecting
cap & hinged at b to the case c of the lamp. In the cap d there is provided a glazed
or otherwise protected aperture or window exposing the lamp to view. By means of
a flap or clasp e, bent at right angles thereto, the said cap engages with the upper
edge of the lamp-case c, so that by tightening the screw g, fitted in the lid fand
terminating in a square or the like at its outward end, the said cap d may be firmly
secured in its closed or "locked" position. Owing to the provision of this protecting
cap d, capable of being turned or folded down, the globe or bulb a of the lamp may,
whenever required, be readily and quickly exchanged. The pole-apertures h are
formed in the front wall of the lamp and are rendered inaccessible from outside by the
cap d placed over them.
is the reserve-light, which, in the form of lamp here shown, is located at the back
of the lamp. It is surrounded by a glass-case k, fitted with a protecting glass, and,
while not in use, is covered over by a cap or lid screwed on to its case.
The lamps or lights a and i are connected in the manner illustrated in Figure 4
and controlled by the switch m placed below the hinge b. The switch is connected
with a ratchet n which prevents it from turning rearwards; and from its periphery
there projects a rose or stop o which in conjunction with another similar stop p
provided on the hinge b serves to hinder the lamp while closed, from being switched
on further, when the reserve light has once been switched into contact. While the

page_text: main light is turned on, the stop o would occupy, say, the position indicated
in Figure 2, whence, by turning the head or button of the switch, it may be brought
to the position in which it is represented in Figure 1, thereby completing the con-
nection of the reserve light. The moment this is done, however, the stop p on the
hinge b, against which the stop o is now resting, will prevent the switch m from being
turned any further, until the lamp is opened and the stop p moved out of engage-
ment with the stop o by turning down the protective cap d; as illustrated in
Figure 3.
Owing to this arrangement, the miner is allowed to make use of the reserve light
connection only once, while any possible attempt on his part to tamper with or abuse
the facilities afforded by such reserve light is effectually checked.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, as communicated to
me by my foreign correspondent, I declare that what I claim is :-
1. An electrical safety-lamp for miners the main feature of which is the provision
of two or more illuminant bodies for the purpose of enabling in the event of an
extinction of one of such illuminant bodies-another to be made use of as a reserve
lamp.
2. An electrical safety-lamp for miners, such as is referred to in the first claim, the
main feature of which is a ratchet mechanism which after the current has been
switched once from one illuminant body to another prevents any further electrical
connection from being made, for the purpose of checking any abusive manipulation
of the reserve light.
3. An electrical safety-lamp for miners such as is referred to in the first and second
claims the main feature of which is a nose or stop (such as o) provided on a switch
(such as m) which, when the said switch has been turned for the purpose of con-
necting the reserve light (i) to the current supply, is locked in position by a nose or
stop (such as p) projecting from the hinge (b) of the protective cap (d) of the main
lamp (a), whereupon it cannot be released until after the said cap has been opened.
Dated this 8th day of March 1898.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.