On the whole tour, particularly at the Descent, we undergo an optical illusion which often seems to be incredible.

The entire ship's crew were undergoing a nervous excitement, of which I can give no idea: they could not eat, they could not sleep--twenty times a day, a misconception or an optical illusion of some sailor seated on the taffrail, would cause dreadful perspirations, and these emotions, twenty times repeated, kept us in a state of excitement so violent that a reaction was unavoidable.

It must be something in the currents, or a sort of optical illusion, because in the last shipwreck one man was saved, and he swore that at the time they struck the rock, they were headed straight for the light.