Lighthouses are important to sea travelers. They have been used for thousands of years to warn ships that they are near land or dangerous rocks. Lighthouses are towers built near the shore or among the rocks. They have a bright beacon of light shining from the top. Long ago metal baskets with burning coal or wood were hung from poles at the top of the lighthouse to produce the warning light. Today a very large lens shaped like a barrel sends a beam of light far out to sea. Sailors learn where lighthouses are located. Each lighthouse has a special signal so that sailors can tell them apart. The lighthouses help the sailors stay safely out to sea, and they also help the sailors stay on course.
The main idea of this paragraph is
1. Sailors watch for light houses.
2. Fire in a metal basket makes a good light.
3. Light houses help sailors.