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Whatever else was certain, Stevenson intended that only
the very best would do for his Bell Rock lighthouse - and
that included the most up-to-date equipment available at
the time. No expense would be spared!
The lightroom contained the 24 reflectors, which were placed
on a rectangular revolving chandelier or frame. The two
major sides had 7 each arranged in 3 rows - from top to
bottom - 2, 3 and 2. The two minor sides, 5 each - 2, 1
and 2. To achieve the red flash of Bell Rock's unique light
sequence, panes of red-coloured glass were placed in front
of each of the reflectors on the minor sides.
When the Northern Lighthouse Board was first set up in
1786, the Com- missioners chose as their first engineer
Thomas Smith, a "tin plate worker in Edinburgh"
and an "ingenious and modest man", who had been
responsible for "lighting-up" much of old Edinburgh.
However, on the lighthouse side of things Smith had long
been in favour of lamps enhanced as reflectors, and for
the first four lighthouses he built and perfected the parabolic
shape, placing inside them a mosaic of mirrored glass to
increase the "reflectivity".
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Reflector showing
the Argand burner
and oil reservoir
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For the Bell Rock, however, the drive for improvement in
parabolic reflectors had moved on. In this instance, the
inside of the reflectors were coated with a silver compound
- a techique which had been proven successfully at Inchkeith.
Each reflector was made from a sheet of copper measuring,
when flat, 26¼ inches square, and weighing about
11½ lbs. Each plate was then moulded (by a "very
nice process of hammering", as Stevenson put it) into
a parabolic shape of 25 inches in diameter and set within
a ring of brass.
During the building of the lighthouse it was Smith who
looked after lightroom operations at the Edinburgh works.
This style of reflector continued until 1849, when Thomas
Stevenson (the father of RLS) developed a completely new
hemispherical lamp with a Fresnel-type lens with prisms
in front.
Oil lamps were introduced into Scottish lighthouses in
the late 1780s. Prior to that date such lighthouses that
were around at the time were lit by coal fires - the Isle
of May at the mouth of the River Forth being the earliest.
Argand-burners were used at the Bell Rock. Invented
by a Swiss, Ami Argand (born Geneva 1755) in about 1781,
they became the preferred illuminant, and by 1820 had been
installed at most of Britain's lighthouses. They had a circular
wick about three-quarters of an inch in diameter housed
within a glass chimney or funnel. Each burner had a cylindrical
fountain (or reservoir) of brass, containing 24 oz of oil
(spermaceti), and had a burning capacity for 18 hours, or
equal, according to Stevenson, to the longest night in the
Shetland Islands to the north of Scotland!
To illustrate Stevenson's thoroughness, and his
attention to detail, he made minor improvements to the reflector/burners.
D. Alan explains: "he included a small tray below the
burner to trap surplus oil and a tiny frost lamp
which was lighted in cold weather to warm the main lamp,
thus to assist combustion 'when the oil was liable to turn
thick.' To ensure accuracy Stevenson had the reflector curves
drawn by Professor Leslie and their moulds made by the optician
Adie."
In 1874, spermaceti oil (and subseqently the vegetable-based
oil colza) was replaced in favour of the "mineral"
oil, paraffin, and it wasn't until 1885 that electricity
was used experimentally in certain lighthouses as the mean
of illuminating the lens.
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The winding mechanism
which controlled the revolving lights and fog warning
bells
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The concept of a revolving light did not arrive until the
late 18th century. Even as early as 1801, Stevenson was
keen to have it for the lighthouse at Pentland Skerries,
but it was Start Point (1806) which ultimately had the honour
of becoming Scotland's first revolving light. The Bell Rock
(1811) was second.
The winding mechanism lay immediately below the light chandelier
within the lower part of the lightroom and on a level with
the Balcony. It consisted of a drum around which a weighted
rope was wound. However, it was not practical to allow the
rope to pass directly though the middle of the House. From
the lightroom it was diverted down the sides of the top
4 apartments, and realigned again at the floor of the Provision
room to contine its drop through the remaining part of the
building.
The action of the descending rope, and the consequent turning
of the drum, gave power to the revolving light. By means
of a series of gears, levers and connecting rods, the chandelier
could be stopped and started when necessary. During foggy
weather the same mechanism also gave action to the hammers
of the fog bells. Each bell weighed 5 cwt!
It took 8 minutes for the light mechanism to complete a
full 360 degrees turn.
The instructions for the maintenance of the above equipment
can be found under "Instructions
for the Bell Rock Light-keepers".
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