Improvements in Optical Revolving-light Apparatus for Lighthouses, Floating Lights, Buoys, Harbours, or for Signalling or other Purposes.
Year: 1893

page_text: Date of Application, 27th Sept., 1893
Complete Specification Left, 7th June, 1894-Accepted, 14th July, 1894
. PROVISIONAL SPECIFICATION.
Improvements in Optical Revolving-light Apparatus for Lighthouses,
Floating Lights, Buoys, Harbours, or for Signalling or other
Purposes.
I ALEXANDER BREBNER of 79 Princes Street Edinburgh in the County of
Midlothian, Civil Engineer do hereby declare the nature of this invention to be as
follows :-
Let A B C D E F, Fig. 1 represent in horizontal focal section an ordinary
revolving lighthouse optical apparatus (composed either of dioptric lenses only, or
of the same together with upper and lower catadioptric rings), which collects
the light from the lamp at O into any number (in this case 6) of beams of rays, the
focal rays in each beam being parallelized as shown at A, the exfocal rays giving
rise to a horizontal divergence dependent on the angle subtended by the diameter
of the flame at points on the inside of the lenticular panels.
m!
A peculiarity of this usual form of apparatus is that the divergence of the beams
of light issuing from the lenses is what is called natural, that is arising solely from
the relation of the dimensions of the flame to the focal distance of the lenses.
Thus if the light-source be small the natural divergence must also be small, and if
a flame of 90 millimetres diameter give a natural divergence of, say, 6 degrees, then
an electric arc light of 10" diameter in the same apparatus will only give
40 minutes of natural divergence. Similarly, in regard to vertical divergence, if a
flame 90 high be replaced by an electric light source 15" high the vertical
divergence will be changed from about 6° to about 1°. Hence the smaller the
dimensions of the light-source in a given size of apparatus, the less the divergence
and the greater the concentration of the rays issuing from the apparatus.
m
In revolving apparatus the duration of flash is proportional to the amount of
horizontal divergence. Hence the substitution of an electric arc of 10 /m diameter
in place of a lamp-flame of 90"/ diameter would reduce the duration of flash to
of its original amount. This might be an evil. On the other hand a simultaneous
reduction of the vertical divergence from, say, 6° to 1° might not be an evil, but
might result in an increase in luminous intensity in the direction in which such
increase can be useful, and so be a gain, it being understood that, if the near sea
were thereby deprived of light, one or two prisms would be made specially so as to
light the near sea suitably, the bulk of the rays being spread from the horizon
inwards to the boundary of the near sea specially lighted.
The invention then consists in the use of panels of diverging straight prisms in
conjunction with revolving-light apparatus, a combination which can be made to
produce artificially any amount of borizontal divergence necessary to give a
sufficient duration of flash, without affecting an advantageous reduction of vertical
divergence as referred to above. The horizontal divergence so obtained artificially
from each straight prism (see L, Fig. 1) has a peculiar feature distinguishing it
from natural horizontal divergence, namely, that it is composed of light of equal
intensity throughout the whole angle of artificial divergence. This equality is
further perfected in the entire beam from each panel by the use of a number of
straight prisms, each of which spreads the light falling on it over the same angle
of artificial divergence, each straight prism thus co-operating with all the others.
The arrangement of the diverging prisms is shown in horizontal section, outside
the usual revolving-light apparatus at K, L, M, Fig. 1, the panels of straight
prisms at N, G, H being suppressed in the figure. One panel of the optical

page_text: combination is shown in elevation in Fig. 2, the straight prisms being shown in
continuous lines.
These straight prisms may be either plano-convex as in Fig. 3, or plano-concave
as in Fig. 4, the required divergence being obtained directly in the latter case and
after a preliminary convergence in the former case.
In certain cases it may be convenient to make the straight prisms suited to bend
the whole angle of divergent rays round an angle such as P, Fig. 5.
The straight diverging prisms may be applied furtlier to every case of the
group-flashing dioptric system introduced by Dr. John Hopkinson and to certain
special modifications of this system suited to signal given numbers of which an
example may be given in the Complete Specification.
I claim the invention whether in the case of completely new apparatus including
the simple revolving-light apparatus and the straight diverging prisms, or in the
case of the addition of the panels of straight diverging prisms to previously
constructed simple revolving-light apparatus.
I claim the invention whatever be the light-source, oil, gas, electricity or the
like, and whatever be the use to which the combination of apparatus described is
applied, lighthouses, harbours, buoys, floating lights, ships, for signalling or other
purposes. But the form of projector which consists of a dioptric lens parallelizing
the rays of a light-source, with diverging prisms in front to spread the parallelized
light over a given angle, and which sometimes has a mirror at the back of the
light-source, is not claimed in this my invention, except in case a similar
combination should be used as a continuously-revolving light, in which case it does
fall within this my claimed invention, unless it be the fact that, contrary to my
belief, such a combination has already been used as a continuously-revolving light
and not merely as a fixed projector, or as a search-light movable but not continuously
revolving.
In case of its being found convenient to apply the panels of diverging prisms
described above only in front of catadioptric portions of the simple revolving-light
apparatus or only in front of the dioptric portion, then such partial uses of the
system proposed by me are claimed as falling within the present invention.
Dated this 26th day of September 1893.
Improvements in Optical Revolving-light Apparatus for Lighthouses,
Floating Lights, Buoys, Harbours, or for Signalling or other
Purposes.
I, ALEXANDER BREBNER of 79 Princes Street, Edinburgh, in the County of
Midlothian, Civil Engineer 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:-
In this Complete Specification I shall refer in the first place to the drawings filed
with my Provisional Specification and afterwards to the additional sheet of
drawings accompanying this present Specification.
Fig. 1. of the drawings left with my Provisional Specification shows
at A, B, C, D, E, F a horizontal focal section of a six-sided optical revolving-light
apparatus of the usual form with its focus at O, which coincides with the centre of
the light-source. Each of the six sides or panels is calculated so as to parallelise
the focal rays that fall on it from O, as shown at G. Practically however the
light-source always occupies a certain space surrounding the mathematical focus O,
and gives rise to an amount of divergence (called natural divergence) which is
greater the greater the volume of the light-source. The natural horizontal.

page_text: divergence of the beam of light proceeding from each panel of the apparatus
suffices, in general, to give a sufficient duration of flash as seen by the mariner each
time the revolving apparatus causes a beam of light to cross his path. The natural
vertical divergence of light should be sufficient to extend from a direction a little
above the horizon inwards to within about a mile from the lighthouse. Generally
speaking all excess of vertical divergence above some such angle as that just
roughly defined serves no useful purpose. The simplest means of obtaining a
highly concentrated beam of light from a flame of given size:consists in surrounding
When this is done
such flame by an optical apparatus of long focal length.
however both the horizontal and vertical natural divergences are reduced
simultaneously. And it may happen that, when the vertical natural divergence
has been reduced suitably so as to avoid waste of light by excessive vertical
divergence, the natural horizontal divergence may have been reduced so much as to
give a flash of insufficient duration. Hence it is sometimes desirable to have a
means of controlling the horizontal divergence of a beam of light proceeding fron
an apparatus without modifying the natural vertical divergence. Again, if it be
desired to produce lighthouse characteristics comprising long and short flashes,
some means of controlling the amount of horizontal divergence independently of the
vertical divergence is necessary for the economical production of such characteristics.
Now the invension which I hereby claim consists in the addition of panels of
vertical diverging prisms to panels of the usual revolving-light apparatus, whereby
the total horizontal divergence of the beams of light emitted can be controlled
without any alteration of the natural vertical divergence of these beams. Three
panels of such vertical diverging prisms are shown in horizontal section at K, L, M
of Fig. 1 of the drawings left with my Provisional Specification, and one panel is
shown in elevation in Fig. 2 of the same drawings; in the elevation the diverging
prisms are shown by continuous vertical lines, the dotted lines representing the
usual revolving-light apparatus outside of which the diverging prisms are placed.
Fig. 1 of the same drawing shows at L how the diverging prisins act on the
parallelised beam of focal rays issuing from panel D of the usual revolving-light
apparatus. For the sake of clearness the natural divergence which arises from the
volume of the light-source surrounding the mathematical focus O is not shown in
Fig. 1, but only the foca! rays proceeding from O. The diverging prisms can be made
to give to the parallelised focal rays any required angle of artificial horizontal diverg-
ence in the manner shown at L, and the total horizontal divergence of the beam emitted
from the compound panel is equal to the sum of the natural horizontal divergence due to
the diameter of the light-source and of the artificial divergence due to the curvature
of the diverging prisms. These diverging prisms may be, in horizontal section,
either plano-convex, as in Figs. and 3, causing the parallelised rays to diverge
after a preliminary convergence, or plano-concave, as in Fig. 4, causing the
parallelised rays to diverge at once. And in certain cases it may be convenient to
shape the diverging prisms as in Fig. 5 so that besides causing the parallelised
rays incident on them to diverge as required they may also cause the axis of the
emitted beam to deviate by any horizontal angle P from the direction of the incident
rays. The diverging prisms may have either their plane or their curved faces turned
towards the revolving-light panels. Since each of the diverging prisms in one
over the
panel co-operates with all the others and spreads the rays incident on
same angle, the resultant angle of artificially obtained horizontal divergence will
be of nearly uniform intensity throughout. In the case of very large apparatus
each panel of the diverging prisms may be made in several compartments, each in
its own metallic frame, and in such case diverging prisms opposite the upper or
lower catadioptric prisms, which give less natural horizontal divergence than the
dioptric or refracting elements, may be made to give more artificial horizontal
divergence than those opposite to the refracting elements, so that the total
horizontal divergence from all parts of the apparatus may be made as nearly as
possible the same.
For the usual heights of lighthouses a vertical angle of 1° is sufficient to take in

page_text: the whole extent of the sea from the visible horizon inwards to the circle of 2 miles
radius described about the lighthouse as centre. Into this angle all but a small
fraction of the light of a lighthouse should be concentrated. The portion of the
sea within the 2 miles radius can easily be lighted by one or two prisms of
the ordinary apparatus specially calculated for this purpose or by other means
which need not be mentioned here. If however the ordinary optical apparatus are
made of such long focal length as to give with the light-source used only 1° of
natural vertical divergence it would in some cases be desired to obtain more than
the corresponding amount of natural horizontal divergence. The diverging prisms
of this invention provide the best means of obtaining the desired increase of
horizontal divergence. And for this purpose the diverging prisms described are
applicable in the case of the usual single flashing dioptric apparatus, in the case of
the group-flashing apparatus proposed by Dr. John Hopkinson, and in the case of
apparatus giving numerical characteristics, one example of which in given in Fig. 1
of the drawing accompanying this Specification. The apparatus shown in this
Figure 1 signals number 12. This figure shows a horizontal focal section of the
apparatus, which is composed of 180° of reflector returning the light falling on it
back through the flame, and of 3 panels of the usual form of revolving-light
apparatus, each panel subtending 60° horizontally at the focus and having a panel
of the diverging prisms placed just outside of it. The horizontal angle between the
axes of panels B and C, belonging to one group, is only 32°, whilst the angle
between the axes of panels B and A, belonging to different groups, is relatively
large, namely, 88%, which shows how the flashes which go to make one digit are
separated from those which go to make another digit of the characteristic
number 12; again a very much longer interval of 240° between the axis of panel C
and that of panel A provides a long interval of darkness separating the end of one
completed indication of the characteristic number from the beginning of the
following indication of the same characteristic number. The impression conveyed
to the mariner by this apparatus as it revolves is represented graphically
by a thick dark circular line with three breaks in it, which represent in
relative position and in duration the flashes, whilst the dark line represents the
eclipses. An arrow shows the direction of rotation of the apparatus. If the
apparatus be supposed to make one revolution per minute the mariner would see
first from panel A a flash lasting I second, corresponding to 6° of divergence, then
an eclipse lasting for 133 seconds, then from panel B a flash of 1 second, then an
eclipse of 4 seconds, and then from panel C a flash of 1 second followed by a very
long eclipse of 39 seconds. Other such numerical characteristics may be obtained
with or without the use of reflectors. It must be specially mentioned that the
invention claimed in such apparatus is not at all the arrangement of the flashes so
as to produce numerical characteristics, but merely the use of the diverging prisms
in connection with this arrangement of the ordinary revolving-light apparatus.
It remains to describe next a series of characteristics of quite a special nature,
namely, characteristics comprising long and short flashes. I do not at all claim the
invention of such groups of long and short flashes, but I do claim the invention of
a particular means of producing them. This means consists in using the simple
panels of ordinary revolving-light apparatus for short flashes, whilst using for long
Hashes compound panels of ordinary revolving light panels in conjunction with panels
of the diverging prisms described above. In order that the intensity of the long
flashes may equal that of the short flashes, which is necessary in order that the
characteristic of the lighthouse may be the same at all distances from which any of
its flashes are visible, the horizontal compass of the panels producing long flashes
is taken as much greater than the horizontal compass of the accompanying panels
producing short flashes as the duration of the long flashes is greater than that of
the short flashes. Thus for example for double duration of flash the compound
panel producing it is taken of horizontal angle twice as great as that of the simple
panel producing the short flash. Thus equality of intensity of long and short
Hashes is obtained. It might be objected that the second agent used in the

page_text: compound panel causes extra loss of light, but, as this extra loss would not
exceed 7 per cent., it may be neglected in practice since a difference of 7 per cent.
in intensity would not cause an appreciable difference in luminous range. Nothing
however prevents the use of compound panels of horizontal compass bearing
proportion to that of the simple panels slightly greater than the proportion of the
long to the short flash, and any such refinement is naturally claimed as falling-
within the present invention.
a.
One illustration of the numerous characteristics obtainable by the use of groups-
of long and short flashes and of the apparatus proposed now for the first time for
producing them is given in Fig. 2 of the drawing accompanying this Specification..
The apparatus shown in horizontal focal section in Fig. 2. is composed of 4 groups
of 2 panels, each group comprising a simple panel of ordinary revolving-light
apparatus subtending a horizontal angle of 30° and a compound panel subtending a
horizontal angle of 60°. The compound panel includes a panel of ordinary
revolving-light apparatus together with a panel of vertical diverging prisms place:
outside it. The simple panel is supposed to give with the flame placed at the
focus 6° of natural horizontal divergence, and the compound panel is calculated so-
as to give a total horizontal divergence of 12°, a double quantity of light being
thus taken to produce a flash of double duration. One group of two panels only of
the glasswork is shown in section, the other three groups being represented by
simple and double lines corresponding to the simple and compound panels. As the
apparatus revolves in the direction of the arrow a group of two flashes, the first
short the second long, is shown at regular intervals. By reversing the order of the
panels, or the direction of rotation, a long-short characteristic is obtained instead
of the short-long just described. As in Fig. 1, so in Fig. 2 the alternating flashes.
and eclipses are represented graphically by a thick black circular line the breaks in.
which correspond to the flashes. In certain cases it may be suitable to use the
diverging prisms along with the panels producing the short flashes as well as with
the panels producing the long flashes and such cases fall also within my claimed
invention.
The optical combination consisting of vertical diverging prisms in conjunction.
with holophotal lenses may have been used previously for lighting given fixed angles
in azimuth, that is as a fixed light, and the same combination has been used for
electric light search lights mounted so that the single beam of divergent light
issuing from them can be directed in various directions at will irregularly, and it
has also been used for fixed projectors on ships, but none of these uses of such a
combination is claimed as part of this invention.
What is claimed as absolutely new is the application of the combination in.
question, in the various ways described in this Specification, to lighthouses, floating-
lights, buoys and harbours for producing revolving lights in which the apparatus.
revolves continuously for a certain time at a uniform speed around one axis,.
producing a characteristic which is repeated at regular intervals. Inasmuch
also as the combination referred to might be used to produce, by continuous rotation.
for a certain length of time, the symbols of the Morse alphabet or those of any
other code, either purely numerical as proposed by Mr. Babbage, or containing
long and short flashes in the letters or symbols, such possible use is also claimed as
falling within this invention.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. The use of diverging prisms of any of the forms shown in horizontal section
in Figs. 3, 4 and 5 of the drawing left with my Provisional Specification in
conjunction with panels of the ordinary revolving-light apparatus so as to control
at will the total amount of horizontal divergence of the beams of light issuing from
such compound panels without altering the natural vertical divergence, whereby I
obtain an apparatus for producing revolving lights in which loss of light from

page_text: excess of vertical divergence can be reduced to a minimum; for, the natural vertical
divergence having been suitably reduced by the choice of a lens of sufficiently long
principal focal length, the vertical diverging prisms allow of the horizontal
divergence being made sufficient to give any desired duration of flash. This use of
the vertical diverging prisms is applicable to all the usual dioptric and catadioptric
revolving-light apparatus whether producing single flashes, or groups of flashes, or
numerical characteristics as illustrated by Fig. 1 of the drawing accompanying this
Specification, or characteristics containing long and short flashes.
2. The use of the said diverging prisms in conjunction with certain of the panels
of revolving-light apparatus arranged in the manner illustrated by Fig. 2 of the
drawing accompanying this Specification, by which manner of arrangement any
number of novel characteristics comprising short and long flashes, preferably of
equal intensity, can be obtained.
3. The use of the said diverging prisms when added to previously constructed
revolving-light apparatus, when for any reason, whether the substitution of an
electric-arc illuminant for an oil or gas illuminant, or any other reason, it is desired
to regulate at will the total amount of horizontal divergence of such apparatus.
4. The use of the said diverging prisms along with revolving-light panels for the
purpose of obtaining very powerful light signals, whether with the Morse or any
other code, by rotation of the combined apparatus at uniform speed about one axis
Dated this 6th day of June 1894.
ALAN BREDNER,
Agent for Applicant.