Legend has it that the Pharos of Alexandria, first and greatest of all lighthouses, had at its summit a huge curved mirror. It was said that, if one looked into it, ships could be seen at great distances out to sea. If that wonderful mirror did indeed exist, it is lost in time as is the great Pharos itself. Let us move, fast forward, through time and space, across the Mediterranean and out through the Pillars of Hercules like a beam of light. The Roman Empire falls and its marvelous stone beacon towers are extinguished and crumble. Head north, past
the unlit coast of Europe in the Dark Ages, when lighthouses might bring more harm than help by attracting the dreaded Vikings. Innumerable ships are born and die, spilling their cargos of tragedy on the shoals and cliffs.
As we fly into the future, north through the English Channel, we see great fires being lit on towers to give faint hope to mariners. The fires become chandeliers of candles and then oil lamps. Great lighthouses are built along the English coast as we begin to slow in our mad dash over time and tide. Now we see before us the spike of the Bell Rock Lighthouse rising out of the ocean in defiance of the terrible waves that sweep against its base. In its lantern room shine Robert Stevenson’s amazing reflectors.
Catoptric light systems inside glass-enclosed lantern rooms were a paradigm shift in lighthouse technology. Before this innovation, lighthouses had not changed much from the time of the Pharos. Open fires atop simple towers were what worked best. Various types of reflectors were in use as early as the 1730s. A reflector of polished silver was installed in a lighthouse in Sweden in 1738. Different types of polished metals such as brass and tin were used. One early reflector had a wooden frame coated with plaster. Facets of mirror glass were imbedded in the plaster. Reflectors of curved mirror glass proved too fragile for use in a lighthouse. Porcelain or earthenware reflectors, with a glaze of silver luster, worked well but the silver came off with cleaning.
Some early reflectors were hemispheres, but a parabolic shape was far superior. A beam of light emitted from a light source at the focal point of a parabolic mirror will be reflected in a horizontal line from any point it may strike on the mirror. Therefore, the maximum amount of light will be reflected out to sea in a concentrated horizontal beam. The main problem with these early catoptric systems was the light source. Until the late 1700s, oil lamps were not much different from those neglected by the seven foolish virgins. Often, mariners would demand a return to the old open fire system. In 1782 Ami Argand, a Swiss chemist, introduced the smokeless oil lamp that bears his name. Coupled with a parabolic reflector it produced the most brilliant light available at that time. As the years went by, different inventors added various improvements. The neck of the glass chimney was contracted just above the flame to direct the current of air onto the flame. The reserve for the oil was mounted higher than the combustion chamber to give a superabundant flow of fuel to the wick.
Stevenson’s reflectors incorporated all of the advantages of previous apparatus plus some modifications of his own. They were constructed by metal smiths who would fuse a sheet of silver with a sheet of copper. A craftsman would then hammer this two-layered sheet of metal into a near-perfect parabolic shape. A bezel of brass was then fitted around the rim of the mirror for strength. The level of craftsmanship required to build these mirrors was remarkable. As Fresnel lenses are sculptures in glass, Stevenson reflectors are works of art in metal. The lamps could be lowered out of the mirror to allow for ease in polishing the reflective surface. The burners were sometimes tipped with silver to protect the wicks from the great heat produced in the lamp’s combustion chamber. An optional frost lamp could be added to keep the oil in the lamp from freezing in winter.
The lamps burned whale oil, specifically spermaceti oil from the echolocation chamber of sperm whales. This was the finest oil of its time. The reserve for the oil was designed to hold enough oil to burn for 24 hours. Stevenson incorporated clockwork-turning mechanisms into his light apparatus. Turning made the lights flash when observed from sea. Varying the speed and number of reflectors made it possible for each lighthouse to have its own unique combination of flashes for easy identification. Some lights would have red glass chimneys on some of the oil lamps, producing alternate red and white flashes. The light at Cape Bonavista in Newfoundland gave two white flashes and then a red flash with a 30-second gap between each flash. Even today the combination of each lighthouse is indicated on sea charts. This allows mariners to identify any lighthouse and find their position from it.
Catoptric lights required constant care. The keeper had to watch them all night long to be sure that they were burning at their brightest, adjusting the wicks when necessary. At sunrise the lamps had to be refilled. The mirrors had to be polished every day. Polishing would require up to two hours of work in some cases. Special care and technique were required to keep from polishing away the silver surface. This must have been mind-numbing, after being up all night watching them.
Catoptric systems were installed in lighthouses along all the coast of the British Isles. Catoptric reflectors were called the English System. With the coming of Fresnel lenses, (the French System) catoptric systems became obsolete. Three sets of reflectors from Scotland were sent to the British colony of Newfoundland, Canada, after lenses had replaced them. The Bell Rock lights first lit in 1811 were sent to Cape Bonavista where they saw service until 1892. The apparatus from the Isle of May, first lit in 1816, was sent to Harbour Grace Island. In 1892 it was moved to Cape Bonavista to replace the Bell Rock apparatus, which had finally worn out. There they provided constant service until 1960, an incredible 145 years of service. Today, the Cape Bonavista Lighthouse is a Provincial Historic Site restored to the 1870s period, and those same reflectors with their clockwork mechanism are on display there. They look as good as they did more than a century ago. If we had some whale oil, we could probably light them tonight.
Don Johnson is the site supervisor for Provincial Historic Sites, Bonavista, Newfoundland, Canada.
This story appeared in the
May 2005 edition of Lighthouse Digest Magazine. The print edition contains more stories than our internet edition, and each story generally contains more photographs - often many more - in the print edition. For subscription information about the print edition, click here.
All contents copyright © 1995-2024 by Lighthouse Digest®, Inc. No story, photograph, or any other item on this website may be reprinted or reproduced without the express permission of Lighthouse Digest. For contact information, click here.