Jerry Dover, age 11, of Tulsa, Oklahoma, for his question:

How is the ocean floor mapped?

This is a long and tedious job and those who do it usually take along other interests to avoid boredom. Most of them are oceanographers, who never have enough time to study the fascinating wonders of the sea and its teeming marine life. The survey ship is fitted with instruments that measure the depth of the ocean bed at first one spot, then another. Much of this work is done and the details recorded automatically. Later, the map makers on board add each series of details on a chart of the ocean bed.

Most of the work is done by a sonar system that uses a beam of sound waves. The ship has instruments to transmit electrical impulses, change them to sound waves and beam them straight down to the ocean bed. From this solid surface they bounce back up and are trapped by a receiver. The two way trip is clocked by a super sensitive time¬piece and compared with the known speed of sound through water. The depth of each point on the undersea chart is estimated from half the time it took the sound waves to go down there and return.