mistake was repaired, and a teaspoonful of oil was poured on its windward side, where the waves were in an incipient state, and the oil could not be driven back on the shore, an instant calmness diffused itself over a space several yards square, which extended gradually until it reached the lee side of the pond, making all that quarter of it, perhaps half an acre, as smooth as a looking-glass. After this, he took with him, whenever he went into the country, a little oil, in the upper hollow joint of his bamboo cane for the purpose of repeating his experiment, whenever he had a chance to do so, and, when he did repeat it, it was usually with success. Far from being so successful, however, was the experiment when, on a blustering, unpleasant day, he attempted, with the co-operation of Sir Joseph Banks and other friends, to still the surf on a shore at Portsmouth with oil poured continually on the sea, at some distance away, through a hole, somewhat bigger than a goose quill, in the cork of a large stone bottle, though the effusion did flatten out a considerable tract of the sea to such an extent that a wherry, making for Portsmouth, seemed to turn into that tract of choice, and to use it from end to end as a piece of turnpike road. All this is described by Franklin in a letter to William Brownrigg, dated November 7, 1773, in which he cited some other illustrations of the allaying effect of oil on waves besides those that we have mentioned, and developed the philosophy of the subject with that incomparable clarity of his, not unlike the action of oil itself in subduing refractions of light. Now I imagine [he says] that the wind, blowing over water thus covered with a film of oil, can not easily _catch_ upon it, so as to raise the first wrinkles, but slides over it, and leaves it smooth as it finds it. It moves a little the oil indeed, which being between it and the water, serves it to slide with, and prevents friction, as oil does between those parts of a machine that would otherwise rub hard together. Hence the oil dropped on the windward side of a pond proceeds gradually to leeward, as may be seen by the smoothness it carries with it, quite to the opposite side. For the wind being thus prevented from raising the first wrinkles, that I call the elements of waves, cannot produce waves, which are to be made by continually acting upon, and enlarging those elements, and thus the whole pond is calmed. And the water in which the Bermudian struck his fish is not more limpid than these observations suggested by the Portsmouth experiment: