nted the story he had heard in Devil's Hole.
The boy rather feared that Early Bird might make light of it even if the
museum curator did not, but the darky remarked that he thought it was a
good thing to let morays alone and that he had heard the story from
other sources before. In the meantime the leader of the expedition had
found a section of the reef which appealed to him and at his request
Early Bird put out a small kedge anchor, holding the boat fast. The wind
had dropped a good deal as the morning wore on and now the little
sailing boat rocked gently over the gorgeous gardens of the sea.

"You told me," the museum official said, "that you were fond of drawing.
Here's a sketch block and some pastel crayons; see what you can do with
them."

Colin lifted his eyebrows in surprise, but he took the sketch block and
pad, hooking his water glass to the side of the boat as directed. His
companion took a large water glass of a different character. It was
right-angled with a lens at the end. In the joint of the angle was a
reflector which threw the image upon a mirror immediately under the
eye-piece.

"What's that for?" the boy asked.

"So that we can look at the reefs at their own level," was the reply.
"No matter how much you allow for refraction and foreshortening, you'll
find it almost impossible to get correct values by studying a reef from
the top only. You know how queer a place looks in a picture that has
been taken from an aeroplane?"

"Yes," the boy answered.

"That's what we've got to avoid here. We are looking down on the reefs
just as an aviator looks down on a city. This glass, however, will give
me the proper perspective. You see I have made it something like a
telescope so that I can add segment after segment and watch conditions
even in fairly deep water. Now I'll show you how I'm going to manage
it."

He took the long L glass with which he was working and fastened it by
little hooks to the direct overhead glass which Colin was using, and as
he did so the boy noticed that the two glasses were so arranged that
they focussed at the same point of the reef, only that one viewed it
from above, the other from the side. A little device worked by a
thumbscrew varied the angle in proportion to the depth.

"Now," he was instructed, "draw in and color--as well as you know
how--everything you see in the field of your glass. You've got all day
to do it in, so there's no need for hurry. Remember, I don't want t