At seven o'clock, accordingly, Sir Henry and I went on, Sir Henry at the bow and I at the stern, and the other two lay down and went to sleep.
For three hours all went well, Sir Henry only finding it necessary once to push us off from the side; and I that but little steering was required to keep us straight, as the violent current did all that was needed, though occasionally the canoe showed a tendency which had to be guarded against to veer and travel broadside on.

What struck me as the most curious thing about this wonderful river was: how did the air keep fresh?
It was muggy and thick, no doubt, but still not sufficiently so to render it bad or even remarkably unpleasant.

The only explanation that I can suggest is that the water of the lake had sufficient air in it to keep the atmosphere of the tunnel from absolute stagnation, this air being given out as it proceeded on its headlong way.

Of course I only give the solution of the mystery for what it is worth, which perhaps is not much.
When I had been for three hours or so at the helm, I began to notice a decided change in the temperature, which was getting warmer.

At first I took no notice of it, but when, at the expiration of another half-hour, I found that it was getting hotter and hotter, I called to Sir Henry and asked him if he noticed it, or if it was only my imagination.