There can be no doubt, of course, that intellectual power must be in operation at one end of the line, otherwise no fish will come to the other; but the puzzle is, by what mysterious process can human intelligence manage to find its way, like electricity, down the line to the bottom of the sea? I have often asked successful fishermen what they did to make the fish bite; but they could seldom give any available answer. Sometimes they said it depended on the bait. “Well, then,” I have answered, “let me take your line, and do you take mine.” But in two minutes after we had changed places, my companion was pulling in his fish as fast as before, while not a twitch was given to my new line, though, just before, the fish appeared to be jostling one another for the honour of my friend’s hook, to the total neglect of that which had been mine, now in high vogue amongst them. There is some trick, or sleight of hand, I suppose, by which a certain kind of motion is given to the bait, so as to assimilate it to that of the worms which the fishes most affect in their ordinary researches for food. But, probably, this art is no more to be taught by description, or to be learnt without the drudgery of practice, than the dexterity with which an artist represents nature, or a dancer performs pirouettes. Uninstructed persons, therefore, who, like myself, lose patience because they cannot catch fish at the first cast of the line, had better turn their attention to something else. Almost the only one I ever caught was during this first voyage across the Atlantic, when, after my line had been down a whole weary hour, I drew it up in despair. It felt so light, that I imagined the line must have been accidentally broken; but presently, and greatly to my astonishment, I beheld a huge cod float to the top, swollen to twice the usual dimensions by the expansion of its sound, as the air-bag is called, which lies along the back-bone. At the depth of eighty or ninety fathoms, this singular apparatus is compressed by the enormous addition of fifteen or sixteen atmospheres. But when the air is relieved of this weight, by approaching the surface, the strength of the muscles proves inadequate to retain it in its condensed form; and its consequent expansion not only kills the fish, but often bursts it open as completely as if it had been blown up with gunpowder.