This story is partially the result of the extensive research and writings of Dr. Max F. Homfeld who developed the article Clockwork Fog Signals that was printed in the National Association of Watch and Clock Collectors (NAWCC) Bulletin of October 1986. Dr. Homfeld was mainly interested in clockworks and the specific clock designs used in tower clocks and in their offshoot, the fog-bell striker. Permission was obtained to use Dr. Homfeld’s research and writings and we have expanded the scope of his research to include a much greater emphasis on the various types of fog signals, and especially fog bells, in use throughout the years.

INTRODUCTION

What do church steeples and fog signals have in common? Well in many cases, a strange “Rube Goldberg” looking machine filled with gears, cables, fan-blades and a giant sledge hammer. We are talking about the tower clockwork in the case of a church and a fog-bell striker in the case of a fog signal.

Many types of fog signals were invented, including cannons, bells, whistles, sirens, steam trumpets, reed horns, etc. This story will concentrate on the uses of bells and bell strikers as aids to navigation.

History of Fog Bells

One of the earliest fog bells was established in 1766 at Nidingen in the Baltic. Drawings show a bell in a wooden tower next to the lighthouse. Another early bell was regularly sounded during fog from the south turret at Bamburgh Castle on the northeastern coast of England starting in 1777.

On February 1, 1811, after the completion of the Bell Rock Lighthouse, the Commissioners of Northern Lighthouses in Scotland issued a “Notice to Mariners” stating: “during continuance of foggy weather and showers of snow, a bell will be tolled by machinery, night and day, at intervals of half a minute”. A similar bell was placed in the Skerryvore Lighthouse off the Scottish Coast in 1844.

By 1820, several other bells had been installed at European lighthouses. In 1838, the pile lighthouse on the Maplin Sands was fitted with a bell. From 1841 onward the installation of bells was approved by Trinity House for lighthouses under its administration.

In 1829, a fog-bell was constructed at Bevertail RI (See story further on under clockwork driven bell striker design)

In 1837, the United States Lighthouse Service experimented with a metal triangle at the West Quoddy Head light station. It was constructed of a metal bar 2 1/8” by 14 ½ feet, bent into shape, and rung by hand…it was not a success. At this time fog bells were mostly still rung by hand.

Several countries experimented with bells for use as fog signals in the mid 19^th century, and there were problems. Mr. Cunningham, of the Northern Lighthouse Board, in Scotland stated that the 2 ¼ ton bell at Howth, Ireland, which was struck four times a minute by a 60 pound hammer, could be heard only one mile to windward against a light breeze during fog. He also reflected that he doubted if the bells at the Bell Rock and Skerryvore lighthouses were ever responsible for saving a single vessel from wreck during fog and said he did not recall a single instance of a vessel reporting that she was warned and put about in fog or ascertained her position because of either bell signal. The American experience was similar; General Duane, U.S. Army, said, “a bell…cannot be considered an efficient fog signal on the sea coast. In calm weather it cannot be heard half the time at a distance greater than one mile, while in rough water the noise of the surf will drown its sound to seaward altogether.”

During 1863 and 1864 Trinity House made a series of fog bell trials that were similar to earlier trials undertaken by the French lighthouse authority. Observations were made about the effectiveness of the different sizes of bells and experiments were made to see if different sizes of hammers produced any improvement in the loudness of a bell. They also experimented to determine whether the use of hemispherical reflectors improved the signal. In addition, the prevailing wind speed and direction was logged during the trials. The results proved that increasing the number of strokes per minute was related to the distances at which a bell signal could by heard: 15, 25 and 60 strokes a minute were in ratio to 1, 1.14 and 1.29 miles. The experiments also showed the audible range of bells could by improved by using a reflector to help concentrate the sound. The trials confirmed the observations made by the French who had placed a reflector behind bell signals in an effort to increase the distance at which they could be heard. It was also found that striking the bell with a hammer was more efficient than swinging the bell and the maximum range of a 1000 pound bell was a little over a mile.

Bell Construction

The official specifications for one type of fog bell were as follows: “The bell is to be composed of tin and copper mixed in the proportion of 22 pounds of pure tin to 78 pounds of pure copper. It is to weigh about 2000 pounds, and be of the design shown in the accompanying drawing. Old metal is not to be used in casting. The bell is to be properly finished and free from defects.”

Bells weighed up to 5,000 pounds although in general, bell weight was between 600 and 2000 pounds. The sound of a bell is not composed of a single note instead it has a range of distinctive harmonics. The bell is designed and cast to produce one specific note, which dominates when the bell is first, struck. This note subsides and is replaced with a ringing hum made from the natural harmonics of the original note. Bells were tuned by removing rings of metal from the inside after casting. The bell tuner struck the bell, using his trained ear and tuning forks to determine the precise amounts of metal to remove to produce a ring with the greatest number of harmonic notes and to produce the precise main note