When the helmet was screwed on, Paul felt a smothering sensation but it soon passed.

Encouraged, he stepped down n the rope ladder over the side of the sloop and slowly slipped to bottom about five fathoms below.

The descent was easy, but bewildering.

When his heavily leaded feet struck on the coral, it seemed to him as if the top of his head was being lifted off.

For the moment he wished to regain the surface, but Scott's advice to keep cool and steady came back to him and he quickly regained control of his nerves.