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Lighthouses
© Zany
Aug 31, 2002
Who would have thought that you could learn something about science from lighthouses? Believe it or not, we can learn something about math (geometry and algebra), physics and chemistry from lighthouses. Take a look at Science and Mathematics of Lighthouses . Lighthouses are composed of various shapes. Identifying them can help us with our geometry. They have a few shapes in there that I am not familiar with (frustum and mastaba). Luckily they provide us with definitions. There are even a few hands on experiments that you can try. Check out the stairway and learn about the golden ratio. Geometry and trigonometry will help us calculate the range (how far out to sea the light shines) of a given lighthouse. The web site provides a brief history of how lighthouses were (are) illuminated. Illumination consists of two parts - the lens used (if any) and the light source. For an overall view of when different light sources and lens came into use, visit History and Other Info for a short summary describing the various sources of light.
It was in 1822 that French physicist Augustin Fresnel invented the Fresnel lens, which changed forever the way lighthouses were illuminated. Up until then, reflectors or parabolic mirrors were used to increase the light source. Another name for this type of system is catoptric . For a short introduction to the Fresnel Lens and a diagram illustrating how it works, click over to Fresnel Lens . Fresnel Lens has a short animation of how the lens works but unfortunately it does not tell one much. The Incredible Fresnel Lens provides a more technical explanation of the lens. The Fresnel design is described here as simply quote ...." a barrel-shaped array of lenses encircling the light source. In the area immediately horizontal to the light source, circular lenses magnified and concentrated the visible light as it passed directly though them. At the same time, above and below the light source, multiple prisms mounted around the periphery of the barrel each collected and intensified the light and redirected it in the same directional plane as the lenses ..." unquote. It increased the intensity of the light so it could be seen farther out to sea. It also allowed for the use of coloured glass and rotation of the optic array (to produce a flashing effect) so that the lighthouse beacons could be distinguished from other onshore lights or other lighthouses in the same area. The Fresnel lens is made in eleven orders (varying in brightness and useful range). The largest is the first order. To get an idea of the size of a first order lens, visit Spring Point Ledge Lighthouse . A first order lens is 8.5 feet high, 6.5 feet in diameter, and weighs 12,800 pounds. WOW. There is a picture of one on the page.
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The copyright of the article Lighthouses in Science Websites is owned by Zany. Permission to republish Lighthouses in print or online must be granted by the author in writing.
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