How?" asked the others.

Colin made no verbal reply; but instead, he was seen to insert his
telescope into the sand-parapet, in such a way that its tube passed
clear through to the other side, and of course commanded a view of the
beach, along which the two forms were advancing.

As soon as he had done so, he placed his eye to the glass, and, in a
cautious whisper, announced that both the horseman and camel-rider were
within his "field of view."

CHAPTER XVII.

THE TRAIL ON THE SAND.

The tube of the telescope, firmly imbedded in the sand, kept its place
without the necessity of being held in hand. It only required to be
slightly shifted as the horseman and camel-rider changed place,--so as
to keep them within its field of view.

By this means our adventurers were able to mark their approach and note
every movement they made, without much risk of being seen themselves.
Each of them took a peep through the glass to satisfy their curiosity,
and then the instrument was wholly intrusted to its owner, who was
thenceforth constantly to keep his eye to it, and observe the movements
of the strangers. This the young Scotchman did, at intervals
communicating with his companions in a low voice.

"I can make out their faces," muttered he, after a time; "and ugly
enough are they. One is yellow, the other black. He must be a negro,--of
course he is,--he's got woolly hair too. It's he that rides the
camel,--just such another as this that stumbled over us. The yellow man
upon the horse has a pointed beard upon his chin. He has a sharp look,
like those Moors we've seen at Tetuan. He's an Arab, I suppose. He
appears to be the master of the black man. I can see him make gestures,
as if he was directing him to do something. There! they have
stopped,--they are looking this way!"

"Marcy on us!" muttered old Bill, "if they have speered the glass!"

"Troth! that's like enough," said Terence. "It'll be flashing in the sun
outside the sand. That sharp-eyed Arab is almost sure to see it."

"Had you not better draw it in?" suggested Harry Blount.

"True," answered Colin. "But I fear it would be too late now. If that's
what halted them, it's all over with us, so far as hiding goes."

"Slip it in, any how. If they don't see it any more, they mayn't come
quite up to the ridge."

Colin was about to follow the advice thus offered, when on taking what
he intended to be a last squint through the telescope, he perceived that
the t