|How could one lighthouse be distinguished from another?|
Years ago, before they had all the sophisticated technology of today--LORAN, radar, sonar, on ship electronics, radio beacons, etc.--ships near shore in the daytime would use lighthouses as a landmark. This use gave them an additional name--a DAYMARK.
Imagine that you are the Captain of a ship sailing along the coast. You need some landmarks to help you find your position. When you look on shore you see a tall red brick tower. Then you sail about forty miles down the coast and you see another round red brick tower--just like the first one. How would you know where you are? This is the way things were along a portion of the Virginia and North Carolina coast in the 1870s. To help the mariner determine his location the Lighthouse Board (which was in charge of lighthouses from 1852-1910) issued an order to have each lighthouse painted in different colors and/or designs. This is the best example of DAYMARKS we can see today.
Cape Henry, VA
Bodie Island, NC
Cape Hatteras, NC
Cape Lookout, NC
Cape Henry Virginia (the tallest cast-iron lighthouse in the U.S. today) was painted in alternating black and white sections. Bodie Island was painted with horizontal bands. Cape Hatteras (the tallest one in the country) was given spiral bands. Cape Lookout was painted in a diamond or checkerboard pattern. On some lighthouses elsewhere the color red has been used to help distinguish them. There are two very striking ones painted in red stripes--at West Quoddy, Maine, and Assateague, Virginia
West Quoddy Head, ME
But, what about nighttime--the most dangerous time to navigate, and the main reason lighthouses exist? You cant see colors or patterns at night, but you can see lights. However, unless there was some way to make each light different you could have the same problem. Early on, in a few places in our country, they built multiple lights (that is, two or three together.) There are twin lights at Cape Elizabeth, Maine and at Thatcher Island, Massachusetts that are still visible today.
Cape Elizabeth, ME
Thatcher Island, MA
On Cape Cod, they built three lights which they call "The Three Sisters of Nauset", no longer in use, but which have been moved to a central location and preserved by the National Park Service for us to see today. Many of the double lights were either torn down or one of the twins was moved to another location. Building double or triple lighthouses was one way to help the sailors at sea determine their location, but it was a very expensive way to do it.
"Three Sisters" on Nauset Beach, MA
Mounting a group of lights on a rotating framework made it possible to produce a special signature (the first flashing characteristic) for each lighthouse, so they could be easily told apart (more on this follows). A group of lights mounted on a rotating frame made a lighthouse look like it was flashing its light on and off.
The invention of the Fresnel (pronounced "Frey Nel") lens in 1822 was probably the most important discovery in lighting technology. As well as enabling man to produce an unlimited number of flashing combinations, it also intensified (brightened) the light so it was much more helpful to the mariner, and could be seen at greater distances.
The Fresnel lens can be compared to a huge lampshade except that it is made of 100s of pieces of beautiful, specially cut glass. It surrounds the lamp bulb, but differs from a lampshade, which concentrates the light downward. This lens, due to its special design, and because it is made of glass, intensifies (brightens) the glow from the light. It takes the rays of light which normally scatter in all directions and bends (refracts and reflects) them, focusing them into a single beam of light, which shines out in a specific direction.
Fresnel lenses are of two types: Fixed--which shows a steady light all around the horizon and Revolving--which produces a flash or a characteristic. The number of flashes per minute depends on the number of flash panels and the speed at which the optic (lens) revolves. (Teacher: See footnote.)
Fixed Fresnel Lens
Rotating Fresnel Lens
Different periods of darkness and light produce a unique flash pattern for each light For example a light can send out a flash every five seconds. or it might have a fifteen-second period of darkness and a three-second period of brightness, or any number of other combinations. The individual flashing pattern of each light is called its CHARACTERISTIC. Mariners have to look at a light list or a maritime chart that tells what light flashes that particular pattern and what color the light is as well. Then they are able to determine their position at sea in relation to the land.
*Note: There was actually one more style for clarification. So as not to confuse young students I elected to leave this off. It is a fixed light varied with flash. However, if your students are particularly precocious, you may elect to use it.
Today aerobeacons are also used to help identify each lighthouse. They, along with the Fresnel lens, are the principle behind the automobile headlight.
Fresnel lenses come in seven commonly used sizes (called orders). The larger ones (1st order), used on major seacoasts, flash a more powerful beam which shines as far as twenty-one miles out to sea. Sixth order lights, the smaller ones, are used in bays where they do not have to shine as far or as brightly.
Most look like a beehive or barrel; some have bullseyes and can contain from two to twenty-four different panels. Those with the fewest flash panels (two) are called clamshell or bivalve lens. A clockwork type mechanism (which had to be wound by hand every few hours before the advent of electricity) is used to make these revolving lenses rotate around the lamp itself to produce the flash. The movement of the lens is timed precisely so the bullseye panel will pass by when a flash is due.
These lenses are really beautiful works of art; most contain hundreds of prisms -- pieces of specially ground, cut and polished glass which, when arranged in a certain way, bend (reflect and refract) the light. Thus all the rays of the light are collected and redirected into a single beam of light. This makes it much brighter and more effective. The lenses themselves can weigh as much as four tons.
There is one light near Boston (Minots Ledge on the killer reef) which flashes out a characteristic of one flash, darkness, then flash, flash, flash, flash, darkness, then flash, flash, flash, or 1-4-3. The people nearby call it the "I Love You" light because it flashes out the number of letters in each of those words.
Another way to distinguish lights is through the use of color. Although most lights have a white lamp, some do use red and others green lights, as well as combinations of the colors.
What happens in fog when the light isnt visible?
Have you ever been out in a car on a dark, stormy, very foggy night? You know how difficult it is to see other cars on the road. Now, picture yourself sailing along a black-looking sea in a thick pea soup fog with no stars shining or moonlight visible. The windshield wipers are working overtime, but the fog blocks the view of the light. In situations like this there is another method of notifying the mariner, using sound. It is called a foghorn. The first one was used in 1719 at Boston light and it was, of all things, a cannon. Can you imagine being a lighthouse keeper and having to fire the canon every hour when there was fog? During a long spell of fog you wouldnt get any sleep. Later they tried various other means of making a noise for warning. Fog bells were used as well as steam whistles and reed trumpets and sirens. The sounds they gave out were generally low-pitched and very mournful--almost like a wail. Each one emitted a specific number of blasts every minute so it could be told apart from all others. Today, an automatic sensor, which detects moisture in the air, turns on the fog signals when needed. There are also soundless fog signals called radio beacons (an electronic device).
These fog signals were not placed everywhere. Although some places experience no fog problems, fog-warning devices are very necessary in New England, on the Pacific Coast, and in Alaska
|The U.S. Lighthouse Society originally designed this packet to furnish teachers with basic information about lighthouses, their purpose, history, operation and technology in a form presentable to young students. with the society's permission the U.S. Coast Guard Historian's Office is posting this modified version with additional photographs and information.|
The U.S. Coast Guard Historian's Office would like to thank Mr. Wayne Wheeler and the other members of The U.S. Lighthouse Society who produced and distributed the original version of this curriculum.
For more information on lighthouses, teachers and students should contact The U.S. Lighthouse Society, 244 Kearny Street, San Francisco, Ca 94108 or consult the lighthouse web pages on The U.S. Coast Guard Historian's web site.
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