“Why do they have some lights flashing and some just a steady glare?” asked Jack when they reached the next room.
“Well, lighthouses to-day can be made to serve a double purpose. They warn mariners of a dangerous coast and by means of flashes they tell vessels which particular light they are near so the seamen know their exact position when they are traveling the coast. This light shows steadily for one minute and then gives a five-second flash. The next light down the coast may give two or three flashes a minute and so on.”
“Do sea captains have to know the flashes of every light along the coast?” queried Jack.
“Indeed they do and a lot more too,” said Mr. Warner.
“What is the candle-power of lighthouse lamps?” asked Ray.
“They vary a great deal,” said Mr. Warner; “this is very small compared with some of our lights. The one on the Highlands, marking the approach to New York Harbor, is said to be of 25,000,000 candle-power. Not long ago we sent one to the Hawaiian Island that had a lens nearly nine feet tall and weighed four tons. It is mounded, or floated rather, on a bed of mercury and makes a complete revolution every twenty seconds, sending out a double flash of 240,000 candle-power. If it were not for the curve of the earth it could be seen more than forty miles.”
“Jiminy, what a light!” exclaimed Jack. “Did you hear that, Captain Eli?” The keeper was just coming up the spiral stairs to go on watch when Mr. Warner completed his statement.
“Yes, that sort o’ makes my little pet up aloft there seem like a taller candle, don’t it?”
“Well, Captain,” said Mr. Warner, “how’s the weather for a clear day to-morrow?”
“Right’s a fiddle, sir,” said the old man.