Strength and precision:
In planning
the lighthouse, Stevenson and Rennie took note of the work of their engineering
forebear, John Smeaton (1724-92).
Stevenson based the initial design on Smeaton’s Eddystone Lighthouse
(completed in 1759), which had a broad base tapering to a slender tower. Smeaton had been inspired by the shape of an
old oak tree that could withstand the storms that toppled less stable
trees. Rennie’s experience now came into
play, as he adapted Stevenson’s design for the rigorous conditions of the Bell
Rock by insisting on a broader base and more gradual slope to deflect the
battering forces of the waves.
Because of the violence of the sea
and the surge of the tides, construction could proceed only in summer, when
storms were less severe, and only during the few hours of low tide when the
rock was exposed. If low tide was at
night, the crew was expected to work by torchlight. Stevenson referred to the craftsmen working
on the reef as ‘artificers’, a word that evokes the skills and adaptability
needed to overcome the destructive forces of nature.
During the earliest days of
construction, the artificers lived on a boat anchored off the reef. Later, they built barracks, perched on stilts
next to the lighthouse and connected to it by rope catwalk, where they lived in
the middle of the stormy sea. One young
man who worked as a smith fell from the catwalk and was swept into the sea and
drowned. He was the only fatality on the
rock itself, although four men died in other incidents related to the
lighthouse construction.
While enduring gruelling
weather and primitive living conditions, the men were engaged in hard labour
and pushing the boundaries of engineering achievement. The foundations (which, due to the pitiless
force of the sea, had to be extra deep) were hacked out of the rock with
pickaxes. These required constant
sharpening, so a forge was set up on the rock, where the smith was often
working knee-deep in water.
Each of the 2,835 blocks of
Aberdeen granite or sandstone had to be cut to precise dimensions. The work included the crucial dovetailing
that would allow them to fit together (as Stephenson said ‘with great nicety’)
in a minutely calculated, interlocking pattern of ‘courses’, or layers. The finished stones were then loaded onto
boats. Out at the rock, they were unloaded
onto rails that encircled the tower, winched up into position by pulleys and
secured with wooden wedges. Ninety
courses of masonry took the tower to a height of just over 31m (102ft); with
the addition of the glass light-room, the finished lighthouse topped out at
35.3m (115 ft 10in).

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