But we made it a rule never to stay long under water at a time.

Jack told me that to do so often was bad for the lungs, and, instead of affording us enjoyment, would ere long do us a serious injury.

So we never stayed at the bottom as long as we might have done, but came up frequently to the top for fresh air, and dived down again immediately.

Sometimes, when Jack happened to be in a humorous frame, he would seat himself at the bottom of the sea on one of the brain corals, as if he were seated on a large paddock-stool, and then make faces at me, in order, if possible, to make me laugh under water.

At first, when he took me unawares, he nearly succeeded, and I had to shoot to the surface in order to laugh; but afterwards I became aware of his intentions, and, being naturally of a grave disposition, I had no difficulty in restraining myself.