Then it is caught by a sort of trigger. At night when the lantern is lighted, the weight is allowed to slide slowly down. That pulls the wheels around and the light flashes.

"You see each lighthouse in this section has a different sort of lantern. That is, some are fixed lights, some are revolving lights, some are red and some are white. Sailors can tell, by the difference in the lights, just where they are, even on the darkest night."

"A lighthouse is quite important," murmured Frank.

"We think so," laughed Lucy.

Then the girl took them up into the light chamber itself, a small room, with glass sides. The glass was really in the shape of lenses, as in an automobile lamp, only it was cut in another form, called a prism, in order to better cast out the direct rays, and magnify them.

Then the girl took them up in the light chamber itself.

The lantern was an oil one, and it burned brightly, for it was kept clean, and the wicks were often trimmed. The boys[Pg 39] were rather surprised to find that it was the glass windows, or prisms, that revolved by means of the clockwork, and not the lantern itself. If the lantern went around it could not be trimmed without being stopped, and this would make a difference in the flashes, Lucy explained, and so confuse the sailors.

[Pg 39]

At certain places in the glass sides of the lantern room, there were blank spaces where no light could flash out, and this gave the proper signal for that part of the coast.

If you will take a pasteboard tube, such as calenders are mailed in, cut two or three holes near the top, making the holes the same distance apart, with blank spaces in between, and set this tube over a candle, you will have a good idea of a lighthouse. Then if you will turn the tube around, with the lighted candle still inside, you will get the effect of a flashing light, such as Bob and his chums were shown.

They were much interested, and stayed in the tower some time, watching Mr. Floyd trim and fill the lamp, to keep it bright.

"This is certainly great!" exclaimed Frank, when they were ready to leave.

"It sure is," agreed Sammy. Then he was unable to restrain his curiosity in spite of what he had agreed with his chums. "Say," he asked earnestly, when they 

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