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OurStory: Life on the Water

Lenses and Lighthouses

Script for the Presentation, page 2 of 3

Slide 7: The parts of the Fresnel lens bend the light so a lot of it points in the same direction. The bending is called “refraction” and happens because light moves diÓĀäerently in air than in the glass of the lens. Refraction also happens in water. Take a look at this animation from Science Net Links (http://www.physicsclassroom.com/mmedia/optics/bp.cfm) and try it yourself at home! Can you “break” a pencil using only a glass of water? (Rough animation of Fresnel lens operation)

Slide 8: About a year after Abbie saved the day, the Matinicus Rock lighthouse

(where she lived) was repaired and Fresnel lenses were added to the towers. The lenses added to the Matinicus Rock lighthouse were “third order,” or the third-largest size of Fresnel lenses made for lighthouses. Look at the chart. How tall were the Matinicus Rock Fresnel lenses? Great! Each one was 4’8“ tall. Is that taller or shorter than you are?(Chart of Fresnel lens orders)

Slide 9: The National Museum of American History has a Fresnel lens in its new exhibition On the Water. This lens is 4’ 8” tall. What order is it? Great! It’s a third order lens. (Chart of Fresnel lens orders)

Slide 10: The lens on display at the National Museum of American History was used at Bolivar Point lighthouse, in Galveston, Texas. In 1915, there was a big storm and some of the people from the town of Galveston went to the lighthouse to get protection from the storm. During the storm, the machine part that rotated the lighthouse lens broke. To warn ships at sea, the assistant keeper turned the huge lens by hand for nearly an hour. For more information about this lens, check out the On the Water online exhibition at http://americanhistory.si.edu/onthewater/collection/TR_335567.html . For more activities and information about Keep the Lights Burning, Abbie and America’s activities on the water, visit http://americanhistory.si.edu/ourstory/activities/water. (Image of Bolivar Point Lighthouse)

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