e things that are likely to be
said are represented by one word. For instance _Coal_, in a mining code,
might mean 'Struck vein at two hundred feet level.' In the other sort of
code, the letters are changed. That is done in all sorts of ways, and there
are various tricks. The way to get at nearly all of them is to find out
which letter or number or symbol is used most often, and to remember that
in an ordinary letter E will appear almost twice as often as any other
letter--in English, that is."

"But won't this be in German?"

"Yes. That's just why I wanted those names Dick heard. They are likely to
appear in any message that was sent. So, if we can find words that
correspond in length to those, we may be able to work it out. Here goes,
anyhow!"

For a long time Harry puzzled over the message. He transcribed the Morse
symbols first into English letters and found they made a hopeless and
confused jumble, as he had expected. The key of the letter E was useless,
as he had also expected. But finally, by making himself think in German,
he began to see a light ahead. And after an hour's hard work he gave a cry
of exultation.

"I believe I've got it!" he cried. "Listen and see if this doesn't sound
reasonable!"

"Go ahead!" said Jack and Dick, eagerly.

"Here it is," said Harry. "'Petrol just arranged. Supply on way. Reach Bray
Friday. Von Wedel may come. Red light markers arranged. Ealing Houndsditch
Buckingham Admiralty War Office. Closing.'"

They stared at him, mystified.

"I suppose it does make sense," said Dick. "But what on earth does it mean,
Harry?"

"Oh, can't you see?" cried Harry. "Von Wedel is a commander of some
sort--that's plain, isn't it? And he's to carry out a raid, destroying or
attacking the places that are mentioned! How can he do that? He can't be a
naval commander. He can't be going to lead troops, because we know they
can't land. Then how can he get here? And why should he need petrol?"

They stared at him blankly. Then, suddenly, Dick understood.

"He'll come through the air!" he cried.

"Yes, in one of their big Zeppelins!" said Harry. "I suppose she has been
cruising off the coast. She's served as a wireless relay station, too. The
plant here at Bray Park could reach her, and she could relay the messages
on across the North Sea, to Helgoland or Wilhelmshaven. She's waited until
everything was ready."

"That's what they mean by the red light markers, then?"

"Yes. They could be on