LIGHTHOUSE ILLUMINATION.
1801-1843.
Early modes of illumination--Facet reflectors and lamps--Silvered
copper reflectors and Argand lamps--Isle of May coal
light--Improvements in catoptric lights--Distinctions
for lighthouses invented by Mr. Stevenson, viz.,
flashing, intermittent, and double lights--Floating light
lantern--Lighting of stage of Covent Garden Theatre--Dioptric
system of lighthouse illumination.
Seeing that, for reasons stated in the last chapter, I was led to give
up the idea of attempting to follow any chronological sequence in this
Memoir, it may perhaps be convenient, before speaking of my father’s
general practice as a Civil Engineer, that I should supplement the
sketch I have given of the Bell Rock Lighthouse by some account of the
other important duties he performed as Engineer to the Commissioners of
Northern Lighthouses--an office which, as we have seen, he held for so
long a period.
The lighthouse towers of the last century, though useful as beacons by
day, were after all most imperfect guides by night. Indeed, the rude
expedients adopted at that early period to give light to the sailor
in a dark and moonless sky, present a very curious contrast to the
modern system of lighthouse illumination--the result of careful study
by modern philosophers and engineers. If proof of this be wanted,
we have only to refer to the twenty-four miserable candles, unaided
by reflectors or any other optical contrivance, which shed their dim
and uncertain light from Smeaton’s famous Eddystone for nearly half a
century after it was built.
But indeed at that early time all lights had not even the advantage of
the glazed lantern which protected the candles of the Eddystone from
the winter’s blast and summer’s breeze; the grand Tour de Cordouan on
the coast of France was then lighted by blazing fagots of wood burned
in an open chauffer, and many of the early lighthouses were open coal
fires.
When Mr. Smith, however, was appointed Engineer to the Scotch
Lighthouse Board, he, as has been already said, came forward as the
advocate of lamps aided by reflectors, a system which he introduced
at Kinnaird Head in 1787; so that the Lighthouse Board of Scotland
never employed any less perfect mode of illumination. These early
reflectors, which had been in use in England, consisted of small pieces
or facets of common mirror glass arranged in a hollow mould and fixed
in their places by plaster of Paris; but soon afterwards the facets of
mirror glass, though forming good instruments for their day, and of
their kind, were discarded, and the reflectors were thereafter made of
copper, plated with silver, and brightly polished.
I am not in a position to say when or by whom these metallic reflectors
were first introduced, or what was their exact form, the question being
invested in some degree of doubt; but it was to the perfecting of these
optical instruments and adapting them to practical use in a lighthouse
that Mr. Stevenson’s attention was early directed. Thus we find him in
1805 reporting as follows:--
“The operations at the Start Point were this season begun upon
Monday the 27th of May, and the lighthouse was finished upon
Saturday the 17th October and the light advertised to be lighted
upon the night of Wednesday the 1st of January 1806. Some nights
before I left Sanday I had the light set in motion, when the effect
appeared to be most excellent; indeed, it must be equal to the
Scilly or Cromer lights, and superior to the revolving light at
Tinmouth: at the former there are twenty-one reflectors, and at the
latter there are fifteen, whereas at the Start Point Lighthouse
I only use seven reflectors, but by altering the motion of the
machinery and construction of the revolving part, I produce the
desired effect.”
And again in 1806:--
“I was late in the season for making all the observations I could
have wished upon the Start Point and North Ronaldsay lights, and
was not very well appointed in a vessel for keeping the sea in
bad weather. I however made a cruise for this purpose, and stood
towards the Fair Isle in a heavy gale of wind, with an intention
to run for Shetland, but the wind shifted, and I stretched towards
Copinshaw, at the distance of about ten or twelve miles to the
westward of Orkney, with both lights in view. The second night
I went through North Ronaldsay Firth to have a west view of the
lights. I put about off Westra, and stood northward with both
lights in view, when it came to blow with great violence from the
s.w., and it was with much difficulty we could regain the coast.
Although on this trip I had rather bad weather, with a heavy swell
of sea, yet it was very answerable for my purpose, and I was upon
the whole much pleased with the appearance of the new light; but
I find, when at the distance of ten or twelve miles, with the sea
running high, the light is seen for rather too short a period, so
that it would be proper to place other seven reflectors upon the
frame at an angle of about 40° to the present reflectors, in the
event of removing North Ronaldsay light.”
I find from his correspondence that my father consulted Sir John
Leslie, the distinguished Professor of Natural Philosophy, and
Alexander Adie, the well-known optician, as to the best mode of
procuring a true parabolic form for the construction of his reflectors,
and having introduced a simple means of withdrawing the lamp from
the reflector, his new catoptric apparatus may be said to have been
completed.
[Illustration: FIG. 4.]
[Illustration: FIG. 5.]
The Bell Rock was the first lighthouse that was illuminated by Mr.
Stevenson’s improved apparatus (shown in section in Fig. 4), where _a_
is the fountain for the oil, _b_ the burner, and the directions of the
incident and reflected rays are represented by dotted lines. In Fig. 5
the reflector is shown in elevation; the lamp is represented as lowered
down from the reflector, which is effected by a sliding arrangement
controlled by a guide,--the object being to allow the lamp to be
removed while the reflector is being polished, and to insure its being
returned to its exact position in the true focus of the reflector.
Perhaps the most valuable opinion that can be quoted as to the utility
of this arrangement is that of Mr. Airy, the Astronomer-Royal, who,
after the apparatus had been in use fifty years, and after having
inspected the lighthouses both of Britain and France, says--“This
lighthouse” (Girdleness, in Aberdeenshire) “contains two systems of
lights. The lower, at about two-fifths of the height of the building,
consists of thirteen parabolic reflectors of the usual form. I remarked
in these, that by a simple construction, which I have not seen
elsewhere, great facility is given for the withdrawal and safe return
of the lamps, for adjusting the lamps, and for cleaning the mirrors;”
and in closing his report he adds, “It is the best lighthouse that I
have seen.”[6]
Notwithstanding the introduction of this improved apparatus at the Bell
Rock in 1811, a coal-fire, which had existed for the long period of 181
years on the Isle of May, at the entrance to the Firth of Forth, still
continued, in 1816, to send forth its feeble and misleading light, and
as it was one of the best specimens of the lighthouses of days now
passed away, it may not be uninteresting to give a short account of it.
The May light was at that period what is called a “private light”--the
right of levying dues on shipping being vested in the Duke of Portland,
who was owner of the island. There were many private lights in
England, but the Isle of May was the only one that still remained in
Scotland, and the Commissioners of Northern Lighthouses, believing it
to be advantageous that so important a light should be placed under
public management, so as to secure for the shipping a better light,
and exemption from the high passing tolls charged by the proprietor,
entered into treaty with the Duke of Portland for the purchase of his
rights. This negotiation resulted in the introduction of a Bill into
Parliament in 1814, authorising the purchase of the Isle of May, with
the right of levying toll, for the sum of £60,000.
So soon as the property came into the hands of the Commissioners they
erected a new lighthouse, and on the 1st of February 1816 the old coal
chauffer was discontinued, and a light from oil with reflectors was
exhibited in its stead. I am enabled from an old plan in my possession
to present the reader with two sketches of the original chauffer light
of the Isle of May.
[Illustration: FIG. 6.]
Fig. 6 is an elevation of the building, with the tackle for raising
the fuel to the top, and its inscription stone over the door bearing
the date 1635. Fig. 7 shows the building in section, with its stone
winding staircase and vaulted chambers, the whole structure apparently
being so designed as to be perfectly proof against fire--a precaution
very necessary for a building dedicated to such a purpose, for it is
recorded that no fewer than 400 tons of coal were annually consumed in
the open chauffer on its top.
[Illustration: FIG. 7.]
It was, as I have said, one of the best coal-fires in the kingdom,
and three men were employed to keep the bonfire burning, so that its
inefficiency as a light was not due to any want of outlay in its
support. But its appearance was ever varying, now shooting up in high
flames, again enveloped in dense smoke, and never well seen when most
required. When Mr. Stevenson visited the island, with a view to its
purchase by the Commissioners, he was told by the keeper, that in
violent gales the fire only kindled on the _leeward_ side, and that he
was in the habit of putting his hand through the _windward_ bars of
the chauffer to steady himself while he supplied the fire with coals,
so that in the direction in which it was most wanted hardly any light
was visible. Nothing can be worse than any variableness or uncertainty
in the appearance of a light. Better far not to exhibit it at all than
to show it irregularly; and the coal lights were so changeable and
destitute of characteristic appearance as to be positively dangerous.
This indeed was too sadly proved by the loss of H. M. ships ‘Nymphen’
and ‘Pallas,’ which on the 19th December 1810 were wrecked near Dunbar,
the light of a limekiln, on the coast of Haddington, having been
mistaken for the coal light of the Isle of May. Fortunately only nine
of their combined crews of 600 men perished; but the vessels, valued at
not less than £100,000, became total wrecks.
During the long period he held the office as Engineer to the Board, Mr.
Stevenson designed and executed eighteen lighthouses in the district
of the Northern Lighthouse Commissioners, many of them in situations
which called for much forethought and great energy. All his lighthouse
works were characterised by sagacity and inventiveness, and exhibit
successive stages of improvement, equally indicative of the growing
prosperity of the Board and of the alacrity and zeal with which their
Engineer laboured in his vocation. Whether we consider the accuracy and
beauty of the catoptric apparatus, the arrangements of the buildings,
or the discipline observed by the lightkeepers of the Northern
Lighthouses, we cannot fail to recognise the impress of that energetic
and comprehensive cast of mind which directed the whole. Acting under
the direction of an enlightened Board of Commissioners, my father may,
with the strictest propriety, be said to have created the lighthouse
system of Scotland. His merits indeed in this respect were generally
acknowledged in other quarters; and many of the Irish lighthouses, and
several lighthouses in our colonies, were fitted up with apparatus
prepared after his designs.
In the course of his labours my father’s attention was much given to
the question of _distinction_ among lights--a matter of the utmost
importance, especially in narrow seas, where many lights are required;
and at his suggestion, the Northern Lighthouse Commissioners fitted up
a temporary light-tower on Inchkeith, in which numerous experiments
having this object in view were made.
[Illustration: FIG. 8.
FIG. 9.]
He was the inventor of two useful distinctions--the _Intermittent_
and _Flashing_ lights. In the intermittent distinction the light is
suddenly obscured by the closing of metallic shades which surround the
reflector frame, and on their opening, it is as suddenly revealed to
sight, in a manner which completely distinguishes it from the ordinary
revolving light, which from darkness, _gradually_ increases in power
till it reaches its brightest phase, and then gradually declines until
it is again obscured; the action of these shades in producing the
intermittent effect is illustrated in Figs. 8 and 9. The _Flashing_
light, by a peculiar arrangement of reflectors, and a rapid revolution
of the frame which carries them, is made to give a sudden flash of
great power, once in five seconds of time, and thus has a distinctive
appearance very different from either the revolving or intermittent
light. For these distinctions Mr. Stevenson received from the King of
the Netherlands a gold medal as a mark of his Majesty’s approbation.
[Illustration: FIG. 10.]
Mr. Stevenson also, in 1810, gave a design for a double light at the
Isle of May, as shown in Fig. 10, in which all lighthouse engineers
will see the embryo of the double light of the present day.
I must not omit to notice his improvement on the lanterns of floating
lightships, now universally adopted, which he introduced in 1807.
Previously to this date the lightships exhibited their lights from
small lanterns suspended from the yardarms or frames. Mr. Stevenson
realised the inutility of such a mode of exhibition, and conceived the
idea of forming a lantern to surround the mast of the vessel, and to
be capable of being lowered down to the deck to be trimmed, and raised
when required to be exhibited. His plan had the advantage of giving a
lantern of much greater size, because it encased the mast of the ship,
and with this increase of size it enabled larger and more perfect
apparatus to be introduced, as well as gearing for working a revolving
light. Fig. 11 shows this lantern, and the following is his description
of it:--
“The lanterns were so constructed as to clasp round the masts and
traverse upon them. This was effected by constructing them with
a tube of copper in the centre, capable of receiving the mast,
through which it passed. The lanterns were first completely formed,
and fitted with brass flanges; they were then cut longitudinally
asunder, which conveniently admitted of their being screwed
together on the masts after the vessel was fully equipped and
moored at her station. Letters _a a_ show part of one of the
masts, _b_ one of the tackle-hooks for raising and lowering the
lanterns, _c c_ the brass flanges with their screw-bolts, by which
the body or case of the lantern was ultimately put together. There
were holes in the bottom and also at the top connected with the
ventilation: the collar-pieces _e_ and _g_ form guards against
the effects of the weather. The letter _h_ shows the front of the
lantern, which was glazed with plate-glass; _i_ is one of the glass
shutters by which the lamps were trimmed, the lower half being
raised slides into a groove made for its reception; _k_ shows
the range of ten agitable burners or lamps out of which the oil
cannot be spilt by the rolling motion of the ship. Each lamp had a
silvered copper reflector _l_ placed behind the flame.”
[Illustration: FIG. 11.]
The reputation of my father’s catoptric apparatus was not, it appears,
confined to those interested in the welfare of the seaman. In 1819,
Mr. Stevenson was waited on by a gentleman passing hurriedly through
Edinburgh, who came on behalf of Mr. Harris, the manager of Covent
Garden Theatre, who was desirous to try catoptric apparatus for certain
stage effects which he intended to introduce in London. The proposal
seems rather to have taken the Lighthouse Engineer by surprise, but on
learning that the gentleman who had favoured him with a call was Mr.
Benson, the famous singer of the day, he wrote the following letter to
Mr. Harris:--
“I had some conversation with Mr. Benson of your theatre on the day
he proposed to leave this for London. The purpose of his visit to
me was to inquire about the reflectors we used in the lighthouses
upon this coast, which are under my direction, as he had some plan
in view for dispensing with the _footlights_ on the stage by the
introduction of reflected light.
“Being desirous to give every facility to Mr. Benson’s views,
I offered him the loan of a reflector, which I showed him; but
from his being on the eve of setting off, and wishing to keep the
discovery, if practicable, for your theatre, I agreed to send it
to you at Covent Garden, and this letter is to acquaint you that a
case containing the reflector and its burner was shipped to your
address.
“You are to understand that there is no charge whatever to be made;
I only request that the reflector may be returned when you have
made your trials. I no sooner learned that I conversed with the
gentleman who sings so delightfully in ‘Rob Roy’ than I felt an
irresistible inclination to oblige him.
“Wishing you every success in the projected improvement in lighting
the stage, I remain,” etc.
The reflector was duly returned by Mr. Harris. The note intimating its
shipment says--“It is an excellent reflector, but it collects the light
too much in one spot for our use; I mean, it does not spread the light
sufficiently about.”
I mention this small matter, not so much because the manager of Covent
Garden Theatre came to Edinburgh to get his information, but to show
that Mr. Harris’s experiment, made in 1819, foretold the result of all
trials that have since been made to light railway stations, public
gardens, and parks, by using lighthouse apparatus, which is designed
to _condense_ the rays of light, and not to _diffuse_ them, and is
therefore inapplicable for such purposes.
* * * * *
The remarks I have made on lighthouse illumination refer to what
is known as the _catoptric_ system, whereby the light is acted on
by _reflection_ alone. The invention of the _dioptric_, system by
Fresnel was first communicated to Mr. Stevenson in a letter received
from Colonel Colby of the Royal Engineers, who had an opportunity of
knowing the benefit of Fresnel’s dioptric light in making certain
trigonometrical observations for connecting the Government surveys of
the shores of England and France across the English Channel. The letter
is in the following terms:--
“TOWER, _1st Nov. 1821_.
“MY DEAR SIR,--I am quite ashamed of having delayed answering your
letter, and thanking you for the communications you sent me for so long
a time. In regard to the lamps, an account will be given of them in the
_Annales de Chimie_ for the next month. The lens is composed of pieces
of glass forming a circle three feet in diameter, ground to three feet
focal length. The lamp is similar to an Argand lamp, having hardly any
other difference, except four concentric circular wicks instead of
one. The external wick is about three inches in diameter. The light
given by the lens is remarkably brilliant. When we were at Folkestone
Hill, the lamp at Blancnez appeared to give about four times the light
of the Dungeness Lighthouse, though the distance of the lamp was nearly
double that of the lighthouse. The only difficulty which occurs to me
in their employment in lighthouses is the small angle to which a single
lens gives light. I think one lens is brilliant for seven degrees, and
could not answer for more than eight or nine degrees.
“The Cordouan Lighthouse is to be fitted up with ten lenses round one
lamp.
“With best wishes to Mrs. S. and your family, ever yours,
“THOS. COLBY.”
The merits of the dioptric system of illumination were brought before
the Commissioners of Northern Lighthouses in Mr. Stevenson’s Report of
December 1821, and, as is well known, it has, with various extensions
and important improvements, been very generally adopted in all cases
where it is applicable to lighthouse illumination.