This column continues to provide excerpts from the “Lighthouse Service Bulletin”, a monthly publication of the Bureau of Lighthouses, U.S. Department of Commerce. The first was issued in January 1912, and it continued throughout the existence of the Bureau. Unedited quotes from Volume III, No. 47, dated November 1, 1927 follow. The Bulletin had as it object “supplying information that will be immediately useful in maintaining or improving the standards of the Lighthouse Service, and of keeping the personnel advised of the progress of work and matters of general interest in the service and in lighthouse work in general.”
Comparison of Cast-Steel and Wrought-Iron Anchor Chain For Lightships – A recent comparison of the wearing qualities of cast-steel and wrought-iron chain has been the subject of a report by the superintendent of the third lighthouse district. The tests covered a period of 526 days for steel and 268 days for iron chain, during which time steel chain was used on various lightship stations. The results indicate that the cast-steel chain, while the cost is 10 per cent more than iron, has wearing qualities 30 per cent greater, strength 33 per cent greater, and weight 4 per cent less than the wrought-iron chain.
Placing of the Subfoundation For Lansing Shoal Lighthouse, Mich. – The sub-foundation of Lansing Shoal, in the northern part of Lake Michigan, 12th Lighthouse District, was successfully sunk at the site on July 24, 1927, in 25 feet of water. The structure consists of four reinforced concrete caissons, each 20 feet wide, 54 feet long, and 21 feet deep, placed “checkerwise” with each other, so as to form a hollow square 74 feet outside dimensions and 34 feet inside. The space inside each caisson is broken up into four pockets by cross walls. They weigh about 500 tons each, and their faces at the water line and of the slab which is to go above are protected against ice for a distance of about 6 feet above and below by steel plates and channels.
The four caissons were made at the large concrete plant of the United States Engineers at Milwaukee, using the same forms which had previously been employed for building the subfoundation for Milwaukee Breakwater Lighthouse.
Centennial Anniversary of Fresnel – Augustin Jean Fresnel, the inventor of the modern lighthouse lens, was born in Broglie, Eure, France, in 1788, and died near Paris in July 1827, a century ago. He was educated as a government civil engineer in the Ecole Polytechnique and in the Ecole des Ponts et Chaussees, and turned his principal attention to optical studies in 1815. Besides his important theoretical work in problems of diffraction, he is chiefly remembered for practical improvements in lighthouse apparatus.
It occurred to him in 1819 that lenses might be substituted for mirrors in directing parallel rays of light, and that such lenses of moderate thickness might be built up into a system. Somewhat similar apparatus had been described by other physicists for concentrating the sun’s rays, but Fresnel was the first to suggest polyzonal lenses for lighthouses. The first lens designed by him was built in Paris, and in 1823 it was installed in Cordouan Lighthouse at the mouth of the Garonne. Soon after this such lenses were adopted in France and other countries, and in 1836 were used by the Trinity House. The first Fresnel lens in this country was installed at Navesink Lighthouse, N.J., in 1841, and is still preserved by this service.
Effect of Weather Conditions On Sound – Experiments have been made on the English coast to show the effect of humidity and temperature on the audibility of fog signals, and these are described in an interesting article by Donald M. Horner for the Nautical Magazine for June, 1927.
The tests were made from North Goodwin Lightship in the approaches to the Thames River, observations being taken under all conditions of the atmosphere, not only by ear by also with sound-recording instruments. It was noted that humidity had a definite effect on the range of sound, the sound being fainter as the humidity decreased. It was also noted that higher temperatures produced increased loudness, and the poorest conditions were found in the type of weather generally known as “oppressive,” when there is little or no air movement and a pronounced haze without clouds.
While the results of these experiments are not conclusive from the nautical stand-point, it was evident that wind, humidity, and temperature will cause the most powerful siren to become inaudible at times and at other times to be heard beyond its usual range.
Instructions To Employees – A new edition of Instructions To Employees of the Service has recently been published, dated July 15, 1927. These supersede those of 1915.
That’s a sampling “From the Bulletin.”Watch this space in future issues of this magazine for more.
This story appeared in the
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