had no idea there were hours for sending out the time," confessed
Dick.

"Indeed there are. It is very important, too, that ships know the
correct time to prevent disasters. There are shore stations whose sole
duty it is to supply to ships the time and their location. Don't you
recall my mentioning such coastal stations?"

"Oh, yes; I guess I do remember now," returned Dick, a trifle
confused.

"What happens if you call a station and nobody answers?" interrogated
Nancy. "I have been meaning to ask. Do you just keep on calling as you
do at the telephone?"

"No, indeed," was the instant reply. "Should you do that you would
cause no end of interference and make yourself a nuisance to
everybody. The rule is that after you have called a station three
times at two-minute intervals you must stop for a quarter of an hour
before you call again. If you happened to be calling a fleet of ships
it is desirable to alter your tune rather than keep repeating the
summons in the same key. It saves time. Merchant ships and coast
stations must, however, be called in the wave length definitely
specified for their use."

"Shipboard stations seem to have more rules than the others,"
commented Dick.

"Not more rules but different ones," Bob said. "You see their nearness
to other ships makes this imperative. Each ship has to take care not
to knock out the apparatus of its neighbor by inconsiderate use of a
high-power current; also it must not cause undue interference. In
other words, a bevy of ships, like a group of persons, must be
courteous to one another. If a ship within a ten-mile radius of
another is receiving signals that are so faint that they are difficult
to distinguish, a neighboring vessel should not complicate matters by
trying to transmit a message until the other ship has received what
was coming in. This rule makes for ordinary politeness, that is all."

"Couldn't the ship waiting to talk send a message in a different wave
length?" inquired Dick.

"Oh, yes; that would be quite possible, if the tune varied enough to
make it perfectly distinct."

"But what about high-power stations?" demanded Walter. "They handle
important stuff and of course cannot keep stopping for other people
to talk. Don't their powerful currents damage the receiving sets in
stations near them? I should think they might even injure their own."

"High-power, or long-distance stations have still another problem to
meet and they meet it in a diffe