IMPROVEMENTS IN THE CONSTRUCTION OF THE LENTICULAR APPARATUS FOR LIGHT HOUSES
Year: 1884

page_text: I DAVID HUNTER BRANDON, Engineer of N° 1 Rue Laffitte Paris, France
do hereby declare the nature of the said Invention for "IMPROVEMENTS IN THE
CONSTRUCTION OF THE LENTICULAR APPARATUS FOR LIGHT HOUSES" to be as
follows:-
Since Fresnel's Invention, the optical part of lenticular light houses is generally
composed first of a dioptrical drum, the vertical profile from which covers about
80 degrees, and second of two catadioptrical parts, placed one above, and the other
below the said central part or drum.
The different elements composing the entire optical system are calculated in such
a manner that the rays of light traversing them are nearly parallelised at their
exit, and the most intense body of them is projected on the horizon, the divergence
due to the volume of the luminous focus being generally sufficient to light up
properly the zone situated between the maritime horizon and the light house.
The luminous rays traversing the dioptrical elements are refracted on entering
and on leaving, whilst those which traverse the catadioptrical elements are besides
reflected. It follows, in respect to the dioptrical part or drum, that if the focus is
raised, its entire body of luminous rays is lowered on leaving the apparatus, whilst,
as regards those passing through the catadioptrical elements, they are on the
contrary raised.
Therefore, if in an ordinary light house lenticular apparatus, the focus is displaced
in the direction of its vertical axis either by raising or by lowering the same, it
follows that the entire body of luminous rays is divided in two parts, one of which
is projected in the zones nearest the light house, and the other thrown upwards,
towards the sky, id est, lost.
This is a very serious disadvantage, for it is certain that it would be on the
contrary very advantageous in foggy weather, to be able to utilise the entire power
of the apparatus by inclining the body of the most luminous rays in the reduced
zone where it would only be visible, for in this manner light houses would be

page_text: rendered efficacious, whilst under ordinary circumstances, they would not render
any service,
The means I have invented to obtain the above-mentioned result, id est, to
project as required in an inclined direction on the horizon, the whole of the
luminous rays projected through the lenticular apparatus, without separating or
dividing them, consists in making the dioptrical drum independant of the two
catadioptrical parts, in such a manner as to admit of lowering the said dioptrical
drum, to the desired extent, at the same time that the luminous focus is lowered,
whilst the catadioptrical parts remain stationary. It follows as a natural con-
sequence that the focal plane of the dioptrical drum thus lowered, must be lower
than the luminous focus, in order that this latter should project its rays
downwards.
In order to be able to lower or to raise the dioptrical drum, without displacing
the catadioptrical parts, it is sufficient that it be of a different diameter, (preferably
a smaller diameter), and to fit it on a special framing which may bear on the
framing of the catadioptrical parts or not, as may be most convenient and which
should be provided with racks or with screws for the purpose of moving it bodily
by means of bevel pinions or by any other mechanical equivalents such as levers,
excentrics, balance weights, springs, etc.
This Invention is applicable to all kinds of lenticular apparatus for light houses,
whatever the number of their elements may be and regardless of their forms and
dimensions and the advantages obtained thereby will increase with the power of
the apparatus and the diminished extent of their divergence. These beneficial
results will therefore be particularly important as regards electrical light houses.
Dated this 28th day of January 1884.

page_text: I, DAVID HUNTER BRANDON, Engineer, of N° 1, Rue Laffitte, Paris, France,
do hereby declare the nature of the Invention for "IMPROVEMENTS IN THE
CONSTRUCTION OF THE LENTICULAR APPARATUS FOR LIGHT HOUSES," and in
what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
This Invention relates to certain improvements applicable to all apparatus for
light-houses of the composite form, including refracting prisms and reflecting or
catadioptric prisms, whether for fixed or revolving lights, and its purpose is to
render them more effective as aids to the mariner during hazy weather, without
diminishing their efficiency under ordinary atmospheric conditions.
In the accompanying Drawing Fig. 1 represents the quarter of a complete
apparatus in internal elevation and indicates by a vertical section the normal
distribution of light.
Fig. 2 represents similar view in which, some of main parts are displaced, with
the view of the distribution of the light in a manner more appropriate, during hazy
weather.
Fig. 8 a plan of the metallic framework of my improved apparatus.
Fig. 4 a diagram indicating the desirability of a change in the mode of
determining the profiles of reflecting prisms when they are movable.
Fig. 5, 6 & 64 diagrams of certain modifications of the said apparatus.
In these Figures the main component parts of a lenticular apparatus are A the
refracting drum, B the upper series of catadioptric prisms and O the lower series
of catadioptric prisms.
For carrying out my Invention, I propose to change the relative diameters of the
actual refracting and reflecting portions A B so as to permit of lowering and of
raising respectively these two portions one within the other; in the most
advantageous applied form of the Invention I reduce the size of the upper
reflecting prisms B to such an extent that their weight together with that of their
metallic framework, shall be sensibly equal to that of a refracting drum, such as A,
extending to a well chosen angular distance above and below the horizontal focal
plane, including its metallic frame-work, and I suspend these two portions, viz. the
upper reflecting portion B and the central refracting portion A in counterpoise
against each other by means of flexible chains in metal or other appropriate
material 1, laid over suitable metallic pulleys 2 which rest on the standards 3 fixed
at their bases to the metal framing of the lower series of reflecting prisms C.
These lower prisms C as well as the luminary remain stationary in order that
the former may serve to direct the light that falls on them continually during hazy
as well as clear weather, to the horizon and thus ensure illumination of the same
at such times, as when the refracting and upper reflecting portions A and B having
been set so as to dip the light that falls on them, the haze suddenly rises; or again
to light the sea out so far as the horizon in certain bearings where there may be
little or no haze while the presence of haze in others has called for the dipping of
the main part of the light.
The refracting and upper reflecting portions A & B of the apparatus having
been balanced as above-mentioned, a movement of descent imparted to the former
will be simultaneously accompanied by a movement of ascent of the latter, and the
luminary remaining fixed in position, there will result a dip in the direction of the
.rays emitted that traverse the two portions A. & B, the position of which has

page_text: c
been changed. This motion communicated simultaneously downwards and upwards
to the refracting and upper reflecting portions A and B respectively causes them
to unite in intensifying the illumination of a limited region surrounding the
lighthouse tower.
When it is required to restore the two portions above mentioned to their normal
position as shown in Fig. 1, a reverse motion is communicated to them.
The said pulleys 2 which connect the said parts of the counterpoised apparatus,
instead of being carried on supports 3 that transmit the weight of the apparatus
to the floor of the light room, may, in some cases, be suspended from the dome
of the lantern. For the purpose of suspending the movable reflecting prisms B
and the refracting drum A, it is preferable to make use of metallic open chains
jointed on pins which run between teeth formed on the circumference of the
pulleys, but any other appropriate kind of chain or strap may be used for the said
purpose.
The movable parts A and B of this improved apparatus may be actuated by
levers, weights, springs, toothed wheel gearing or other appropriate mechanical
agents driven by hand, steam or other power. In case a lever is adopted it can be
conveniently attached to the roof of the lantern; if recourse is had to multiplying
bevel wheels, the movement can be advantageously applied to the upper ring 4 of
the upper cupola B of the reflecting prisms.
In Fig. 3 it will be seen that in order to provide entrance for the attendants into
the apparatus as well as for the luminary, one of the six suspending pulleys 2 placed
at angular distances of 60° round the vertical focal axis 5 has been suppressed, that
an opening of sufficient breadth for introducing or withdrawing an electric lamp or
other appropriate luminary has been left in the refracting drum A and that a
60° panel of lower reflecting prisms 6 has likewise been suppressed. Thus the
upper cupola only B is complete in this design. The vertical settings 7 of the
refracting drum A which face each other on opposite sides of the opening in the
same, can be connected by binged metallic bars, so as to reduce the drum, except
at the moments of entering or withdrawing the luminaries to a rigid cylindrical
body. When desired the suppressed lower reflector panel 6 can be restored in the
form of a hinged door.
11
This Invention likewise necessitates a change in the mode of determining the
profiles of the movable reflecting prisms C, see Fig. 4, in which F represents the
focus and A, B, C, & A₁ В₁ C₁ two adjacent prisms calculated in the usual
way, with a view of avoiding superfluous glass and so that F B₁ travels
along BA in the prism and passes out along An C₁ so as to graze past the
corner C, of the underlying prism, while ray F A₁ similarly grazes past B₁, the
innermost corner of the underlying prism. Since in the new form of apparatus
adapted for this Invention, however, the position of the focus F relatively to that
of the reflecting prisms varies and would give rise, if the usual profiles were
employed, to a loss of the angle of light m F¹n if the focus were relatively higher
and at F¹, and a loss of the angle of light r F B₁, which would be directed towards
the sky, if the focus F were relatively lower and at F1, the reflecting prisms B in
the apparatus embodying this Invention shall be calculated so as to prevent loss
of light arising from changes in the position of the luminary in regard to
the same.
It may be observed in Fig. 1 representing the normal distribution of light that
the two lowest prisms of the upper cupola do not act, as they are not in a position
to receive light from the focus; in Fig. 2, however, representing the distribution of
light during haze, these two prisms do, as a consequence of the changed position of
the movable part of the apparatus, receive light, which they direct upon the sea
instead of allowing it to be lost, as would arise if they were not there to intercept
it. These prisms I call supplementary prisms, and without them the Invention
would be defective.
This Invention is not necessarily confined to the form of apparatus above
:described and illustrated in Fig. 1, 2 & 3 as it may be modified in various manners,

page_text: for instance as shown in Fig. 5 the apparatus of a fixed or a revolving light in
which either the upper series B or the lower series C of reflecting prisms can be
suppressed and the remaining one placed in counterpoise against the refracting
drum A; or again as in Fig. 6 representing an apparatus for a fixed or for a
revolving light in which the refracting drum A only is adapted for being raised
or lowered, in which case, it is balanced by a weight 8 suspended by a chain 1
passing over a pulley 2, or as in Fig. 64 in which the refracting drum A is raised
and lowered by clock work actuating pinions 9 working in racks 10 attached under
the drum; or again by making any one or both of the reflecting portions B and C
movable, whilst the refracting portion A remains fixed.
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 :-
First. A lenticular apparatus for light houses in which the relative diameters of
the refracting drum and of the upper series of catadioptric prisms are such as to
admit of the former being raised and lowered within the latter and of a similar
motion being imparted to the latter externally of the former in the manner and for
the purposes above described and illustrated in Fig. 1, 2 & 3 of the accompanying
Drawing.
Second. Equalizing or balancing the respective weights of the two movable
parts A and B in the manner and for the purposes above described.
Third. The suspension of the equilibrated portions in movable inter-dependance
in such a way that by applying a force not much exceeding that necessary to
overcome frictional resistance, an opposite vertical movement is simultaneously
imparted to the two parts, so that they unite optically in dipping or raising the
light incident on them from the focus, in the manner and for the purposes above
described and illustrated in Fig. 1, 2 & 3 of the accompanying Drawing.
Fourth. A mode of determining the profiles of the movable catadioptric prisms,
in order to make them (for all positions they are likely to assume) as efficient in
usefully intercepting light from the focus, as are the catadioptric prisms hitherto
made and destined to be fixed in position relatively to the luminary, as above
shown to be necessary by reference to Fig. 4.
Fifth. In a lenticular apparatus such as above described, the addition of
supplementary catadioptric prisms between the refractor and the upper cupola,
which do not act in ordinary circumstances, but come into play when the refractor
is lowered beneath its normal position in the manner and for the purposes above
described and illustrated in Figures 1 & 2.
Sixth. The modifications of my improved apparatus as above described and
illustrated in Figures 5, 6 & 6ª of the accompanying Drawing.
Seventh. My improved apparatus, or any of its modifications, in combination
with a movable light source.