THE MOST POWERFUL ELECTRIC LIGHTHOUSES OF THE WORLD
In a previous chapter I have mentioned that, although oil is the most
popular form of illuminant in lighthouse engineering, electricity is
maintained to be preferable, but labours under one heavy disadvantage
which militates against its more general adoption. It is expensive
to install and to maintain. Under these circumstances the system has
been restricted to lights of the most important character, preferably
landfalls or beacons indicating the entrance to a harbour. Thus, we
have the Lizard at the entrance to the English Channel; St. Catherine’s
on the Isle of Wight; the Rothersand at the entrance to the Weser; the
Heligoland flaring over the island of that name; the Isle of May at the
entrance to the Firth of Forth; Cape Héve near Havre; and the Navesink
light on the highlands of the New Jersey coast, to guide the mariner
into New York harbour.
The first attempt to apply electricity to lighthouse illumination
was made in the year 1859, by the Trinity Brethren, on the strong
recommendations of Professor Faraday, who was then scientific adviser
to the British lighthouse authorities. The South Foreland light was
selected for the experiments, and the magneto-electric machine invented
by Professor Holmes, who subsequently perfected the siren, was used.
The installation was built with extreme care, as the imperative
necessity of reliability, owing to the peculiar nature of the
application, was recognized very fully. The large wheels made
eighty-five revolutions per minute, and at this speed produced a very
steady light. On a clear night, owing to the elevation of the cliff
the light was visible for over twenty-seven miles, and could be
descried readily from the upper galleries of the lighthouses on the
opposite French shore. In order to determine the relative value of
electric lighting in comparison with the other methods of illumination
then in vogue, another light emitted by an oil-lamp, with reflectors
characteristic of the period, was burned simultaneously from a point
below the top light, so that passing mariners were able to compare the
two systems of illumination under identical conditions.
The French lighthouse authorities were not dilatory in adopting the
new idea, and electricity was installed in the Cape Héve lighthouse in
1863. The light was brilliant for those times, being approximately of
60,000 candle-power. The French investigators then embarked upon an
elaborate series of experiments, and in 1881 an electric light of about
1,270,000 candle-power was established at the Planier lighthouse, near
Marseilles. The investigations culminated in the great achievement of
M. Bourdelles, who, while engineer-in-chief of the Service des Phares,
designed a new electric installation for the Cape Héve light, of
25,000,000 candle-power.
Meantime British engineers had not been idle. In 1871 Messrs.
Stevenson, the engineers-in-chief to the Commissioners of Northern
Lighthouses, advocated strongly the establishment of an electric light
upon the Scottish coast; but it was not until 1883 that the Board of
Trade sanctioned the sum necessary to complete such an enterprise,
and suggested that the innovation should be made at the Isle of May
lighthouse, as being the most important on the East Scottish coast.
This is one of the historic light-stations of Scotland. Lying in
the Firth of Forth, five miles off the Fifeshire shore, the islet
obstructs a busy marine thoroughfare. For 276 years a light has gleamed
from its summit, the change from the coal fire to Argand lamps with
reflectors having been made by Thomas Smith, the first engineer to
the Commissioners of Northern Lighthouses, when this body assumed its
control in 1816. Twenty years later it was converted to the dioptric
system, with a first-order fixed light apparatus having a four-wick
burner. This arrangement was in service for half a century, when it
was converted to electricity in conjunction with a dioptric condensing
apparatus.
The electric installation was designed throughout by Messrs. Stevenson,
and it possesses many ingenious and novel features to this day, while
it was the pioneer of modern electric lighting systems as applied to
lighthouse engineering. Although marked improvements have been effected
in electrical engineering and science since its completion, it still
ranks as one of, if not the, most powerful electric lighthouses in the
world. The beacon is a prominent edifice on the summit of the island.
The building is somewhat pretentious, rather resembling a battlemented
castle than a warning for the mariner, the optical apparatus being
housed in a square turret rising above the main part of the building.
When electric illumination was adopted, the existing accommodation for
three keepers was found insufficient, while a generating-station was
necessary. Instead of extending the old building to accommodate the
additional facilities, a second station was built at a low-lying point
near the sea-level. This contains the engine and generating house,
together with quarters for three more keepers and their families. This
decision was made because at this point, 810 feet away and 175 feet
below the lighthouse, there is a small fresh-water loch whence water
is available for the boilers and condensers, while a marked saving in
the cost of handling fuel as well as of the haulage of the building
materials and machinery was feasible. The current is led from the
power-house to the lighthouse by means of overhead copper conductors.
Some difficulty was experienced in securing electrical apparatus
suited to the searching exigencies of lighthouse engineering, and the
designers made one stipulation, which at first appeared to baffle
fulfilment. This was the placing of the positive carbon below, instead
of above, so as to enable the strongest light to be thrown upwards, to
be dealt with by the upper part of the dioptric apparatus, whereby it
could be used more effectively. One firm struggled with this problem
for many months, and then was compelled to admit defeat, as time for
further experimenting was unavailable, since the lighthouse was almost
completed. Accordingly, the designing engineers had to revise their
plans, and had to acquire alternate-current De Meriten machines,
which, although more expensive and less powerful than those originally
intended, yet were, and are still, wonderfully steady in working, while
they had previously proved highly efficient for lighthouse service.
Two generators of this description were secured, and they constituted
the largest that had been made up to this period, each plant weighing
about 4½ tons. Each machine has sixty permanent magnets, disposed in
five sets of twelve each, while each magnet is made up of eight steel
plates. The armature makes 600 revolutions per minute, and develops an
average current of 220 ampères.
The installation is so designed that one-, two-, three-, or
four-fifths, or the whole, of the current can be sent from each unit to
the distributor for transmission to the lantern, or the two machines
may be coupled and the full current from both utilized. The current is
conveyed to the lantern through copper rods 1 inch in diameter, and
this was the first occasion on which such conductors were utilized for
lighthouse work. There are three lamps of a modified Serrin-Berjot
type, one being in service, and the other two held in reserve. By
means of a by-pass, or shunt, a large percentage of the current is
sent direct to the lower carbon, only a sufficient amount to regulate
the carbons being sent through the lamp. The carbons used are about 1½
inches in diameter, though two-inch carbons can be employed when both
machines are running, and the rate of consumption is 1¼ inches, or,
including waste, 2 inches, per hour. The power of the arc thus obtained
with the current fed from one generator is between 12,000 and 16,000
candles. In the event of the electric installation breaking down, a
three-wick paraffin oil lamp is kept in reserve, ready for instant
service, and it can be brought into use within three minutes.
[Illustration:
_By permission of Messrs. Siemens Bros. & Co., Ltd._
THE ELECTRIC SEARCHLIGHTS OF THE HELIGOLAND LIGHTHOUSE.
On the lower level are three projectors spaced 120 degrees apart. Above
is a fourth searchlight revolving three times as rapidly as those
below.]
The dioptric apparatus, designed by Messrs. Stevenson, and manufactured
by Messrs. Chance Brothers and Co. of Birmingham, is of a novel
character, inasmuch as the condensing principle has been carried to a
pronounced degree. The light characteristic is four brilliant flashes
in quick succession every thirty seconds. The lenticular apparatus
also includes the ingenious idea advocated by Mr. Thomas Stevenson, an
earlier engineer-in-chief to the Northern Commissioners and perhaps the
greatest authority on lighthouse optical engineering, whereby the light
may be dipped during a fog. Thus, in clear weather the strongest part
of the ray may be directed to the horizon, while in thick weather it
can be brought to bear upon a point, say, four or five miles away. The
flashes are produced by a revolving cage of straight vertical prisms,
which enclose the fixed-light apparatus. This cage makes one complete
revolution every minute, the rotary movement being secured through a
train of wheels and a weight, which has a fall of 60 feet in a tube
extending vertically through the centre of the tower, the mechanism
being wound up once an hour by manual effort.
The beam of light obtained by the aid of electricity is of intense
brilliancy and penetration. Its equivalent in candle-power is somewhat
difficult to determine, because the methods of calculation are
somewhat arbitrary and misleading. By their own method of calculation,
the engineers responsible for the installation rate it at 3,000,000
candle-power with one generator in use, and 6,000,000 candle-power when
both are going. This is from 300 to 600 times as intense as the oil
light which was superseded. By another method of calculation the beam
is of 26,000,000 candle-power, while another principle of rating brings
it to upwards of 50,000,000 candle-power. In clear weather the light
has a range of twenty-two miles, being indistinguishable at a greater
distance, owing to the curvature of the earth; but the flashes of
light illuminating the clouds overhead may be picked up forty or fifty
miles away. The total cost of electrifying the Isle of May light
was £15,835, or $79,175; while the annual cost of maintenance is over
£1,000, or $5,000.
The most famous English electric lighthouse is that of St. Catherine’s,
in the Isle of Wight. This point, like the Isle of May, has been a
beacon for centuries. Its creation for this work even antedates its
northern contemporary, because in the fourteenth century a chantry was
built by a benevolent knight on the highest point of St. Catherine’s
Downs, who furthermore provided an endowment for a priest “who should
chant Masses and maintain a burning light at night for the safety of
mariners.” But this protection fell into desuetude.
The station, however, was revived upon the old site in 1785, but it
had to be abandoned, because it was found to be built at too high
an elevation. It was so often enveloped in fog as to be useless, or
at least unreliable, to the seafarer. A new tower, accordingly, was
erected at a lower level, and brought into service in 1840, the warning
rays being thrown from a height of 134 feet above the water. Oil was
used with a burner of six rings, the light being officially known as a
“fixed oil light of the first class,” while the beam was diffused over
an arc of 240 degrees. In the middle eighties the Brethren of Trinity
House decided to bring it up to date, and selected electricity as the
illuminant, at the same time changing the light from the fixed to the
revolving class, with a five-second flash once every thirty seconds.
[Illustration:
_By permission of Messrs. Siemens Bros. & Co., Ltd._
THE HELIGOLAND LIGHTHOUSE.
One of the most powerful electric beacons in the world. Its maximum
candle-power is 43,000,000.]
The installation is not widely dissimilar from that used at the Isle
of May. It comprises two De Meriten dynamos in duplicate, while the
lamps are of the modified Serrin-Berjot type, using carbons, not of
circular section, but with fluted sides. This shape was introduced by
Sir James Douglass, who contended that the former type did not produce
the requisite candle-like steadiness of the flame so essential to
lighthouse illumination. The dioptric apparatus was of the sixteen
panel type, so that the rays were thrown out in sixteen brilliantly
white horizontal spokes. To one approaching the lighthouse at
night-time, the effect in the sky was somewhat curious. It recalled a
huge and illuminated cart wheel or Catherine wheel, lying flat on its
side, throwing its rays to all points of the compass in a steadily
moving circle. This practice had been borrowed from the French, who
went so far as to introduce a twenty-four panel system, and, as in
France, the St. Catherine’s light, when first brought into service, was
not a complete success. The French considered that, by distributing the
light through as many panels as possible, the question of bringing the
flashes into action at short intervals would be facilitated, ignoring
the fact that by so doing the intensity of each ray was impoverished.
In other words, with the twenty-four panel light each panel only
received and threw out one-twenty-fourth part of the volume of light
emitted by the arc. Similarly, in the St. Catherine’s light only
one-sixteenth part of the light produced was thrown through each panel.
A few years ago the optical system was replaced by an apparatus having
fewer panels. The light thrown from the Isle of Wight pharos, with its
beam exceeding 5,000,000 candle-power, represents a marked advance upon
the oil light which it displaced, and certainly it ranks as the most
brilliant light in the English Channel.
A few years ago another magnificent light was brought into service in
the North Sea by the installation of electricity in the lighthouse
of Heligoland. With characteristic Teuton thoroughness, the Germans
discussed the question of the illuminant for this beacon in all its
bearings, and resolved to introduce the most powerful light possible.
This decision was influenced by the dangerous character of the waters
washing the island, as it is flanked on all sides by highly perilous
ridges and sandbanks, which must become accentuated owing to the heavy
sea-erosion that prevails.
The German authorities investigated the various electrical
installations that had been laid down for lighthouse work, with a view
to discovering the most suitable system, the advantages and defects
of existing electric lights, and how the drawbacks might be overcome
most successfully. Meantime the famous Siemens firm discovered a means
of grinding glass mirrors into parabolic form, and this discovery was
accepted as the solution to the problem.
In this type of mirror the back is silvered. The metallic polished
surface is protected completely from mechanical injury and from all
possibility of tarnishing. The inventors claim that mirrors so prepared
are able to compete successfully with lenses and totally reflecting
prisms--in fact, it was maintained that the silvered glass parabolic
mirror possessed the advantages of greater reflecting power and
enhanced accuracy, with less divergence of the beam of light.
Owing to the perfection of the lenses and prisms system of lighthouse
optics, the introduction of arc lights in conjunction with parabolic
mirrors was received with considerable hesitation. In order to dispel
these doubts, the above-mentioned firm forthwith embarked upon an
elaborate series of comparative tests at Nuremberg to ascertain the
relative value of the two systems, and as a result of these experiments
they concluded that quite as good an effect is obtainable with the arc
and parabolic mirror as with the best examples of any other method.
Accordingly, the authorities decided to install the system in the
Heligoland lighthouse. They stipulated that the intensity of the beam
of light should be at least 30,000,000 candle-power, with a maximum
current of 100 ampères. The duration of the flash was to be one-tenth
of a second, followed by eclipses of five seconds’ duration.
The electrical engineering firm entrusted with the contract fulfilled
these conditions by mounting three searchlights spaced 120 degrees
apart upon a rotating platform. That is to say, each light is projected
outwards from a point equal to a third of the circumference of a
circle. The mirror diameter was settled at 75 centimetres (29½ inches)
and the focal length at 250 millimetres (10 inches), the current being
taken at 34 ampères when the table made four revolutions per minute.
Subsequently a fourth searchlight was introduced into the apparatus,
for the purpose of practical experiments and observations concerning
the duration of the light-flash. This fourth unit was mounted above the
three searchlights, but in the axis itself. It is so disposed that its
flash comes midway between any of the two below, and it is arranged to
rotate three times as quickly as the main group of lights. Accordingly,
the duration of the flash thrown from the fourth searchlight is only
one-third of the flash thrown by the others--that is, one-thirtieth of
a second. This lamp is provided with all the necessary mechanism for
keeping it in steady rotation at the increased speed, and for drawing
current from its feed-cable.
Before the installation was placed in the lighthouse at Heligoland,
it was submitted to searching tests at the Nuremberg works of the
builders. These trials proved that with a current of only 26 ampères
the average intensity was as high as 34,000,000 candle-power, with a
maximum of nearly 40,000,000 candle-power; while with 34 ampères the
average intensity rose to approximately 40,000,000, with a maximum of
nearly 43,000,000 candle-power. Accordingly, the terms of the contract
were fulfilled completely.
The searchlights throw their rays from a massive conical tower, the
focal plane of which is 272 feet above sea-level. In average weather
the rays are visible at a distance of twenty-three nautical miles, and
under the most advantageous weather conditions visibility is limited
only by the curvature of the earth, although on a clear night the
light is seen from Büsun, which is about thirty-five miles away. The
Heligoland electric light ranks as a remarkable development in the
application of electricity to lighthouse illumination, but it never has
been duplicated. The cost of maintenance--about £1,400, or $8,000, per
annum--is an insuperable handicap.
On the other hand, the Hornum electric light, which is the most modern
of its type in Germany, is more economical, although by no means so
powerful. The tower is of cast-steel, and carries two electric lights;
while about half a mile distant is a second tower, which throws a
third electric light. In the main tower, on the ground floor, is
installed the electric generating plant (in duplicate), together with
all accessories, such as switchboards, etc. The floor above is devoted
to housing 100 accumulators, which are charged during the day. This
task can be completed by one generating set in about six hours. A
single charge is sufficient to keep the three lights going for ten or
eleven hours, and the lights are controlled by a simple throw-over
switch. By this arrangement the cost of the maintenance of the light is
reduced very appreciably, as only one keeper is on duty at a time, the
station being equipped with two men, who have proved adequate for the
purpose.
Above the accumulator-room is the storeroom and a general workshop,
followed by a bedroom and above that the service-room. As only one
keeper is on duty at a time, he is provided with ample devices whereby
he can summon his comrade in times of emergency; the generating
machinery is also controllable from this floor. From the service-room
the lower light-room is entered. This is a secondary or back light
in the range, the front light being in the tower half a mile away.
Each of these two light-rooms is fitted with two 150 candle-power
incandescent electric lights, but only one is burned in each set at a
time: the second is a reserve. Should the light in action fail from
any cause, although the keeper is warned of the occurrence, he does
not have to stir a finger to bring the reserve light into service.
The short-circuit produced by the accident to the light automatically
revolves the table upon which the lamps are mounted, swings the reserve
light into focus, and then sets it going.
Above the secondary light in the main tower is the principal beacon,
comprising a brilliant rapidly-flashing light, the characteristic of
which is groups of two flashes alternating with four flashes, the cycle
being completed once in thirty seconds. The optical apparatus has been
devised especially for the “differential arc-light,” as it is called,
with a reflecting lens having a focal distance of 250 millimetres
(10 inches), the lens itself being 1,180 millimetres (approximately
47 inches) in diameter. In front of the lens is placed a disperser,
having a diameter of 1,200 millimetres (48 inches) whereby the ray of
light is dispersed through an arc of 10½ degrees. Before the disperser
is the means for producing the characteristic flash. This comprises a
blind, or shutter, which is opened and closed by mechanism adjusted
to requirements; while the rotating mechanism, instead of being
weight-driven, is actuated by an electric motor.
The “differential arc,” which is utilized in this installation, is
considered by German engineers to be the best system that has yet been
devised for the exacting purposes of lighthouse engineering, and the
description has arisen from the disposition of the carbons. While the
positive carbon is held horizontally, the negative carbon is placed at
an angle of 70 degrees thereto, and only the crater of the positive
carbon is considered for the lighting effect, this being placed in
the focus of the apparatus. The positive carbon is 3/5 inch, and the
negative carbon 2/5 inch, in diameter, although both have a common
length of 19 inches, which is sufficient for nine hours’ service. The
beam emitted is of some 5,000,000 candle-power. This is one of the
cheapest electric stations at present in operation, the annual running
charges averaging less than £300, or $1,500.