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again exposed to the air, will soon imbibe an equal quantity.
Therefore, air in motion, which is wind, in passing over the smooth surface of water, may rub, as it were upon that surface, and raise it into wrinkles, which, if the wind continues, are the elements of future waves.
The smallest wave once raised does not immediately subside, and leave the neighbouring water quiet: but in subsiding raises nearly as much of the water next to it, the friction of the parts making little difference. Thus a stone dropped in a pool raises first a single wave round itself; and leaves it, by sinking to the bottom; but that first wave subsiding raises a second, the second a third, and so on in circles to a great extent.
A small power continually operating will produce a great action.
A finger applied to a weighty suspended bell can at first move it but little; if repeatedly applied, though with no greater strength, the motion increases till the bell swings to its utmost height, and with a force that cannot be resisted by the whole strength of the arm and body. Thus the small first-raised waves, being continually acted upon by the wind, are, though the wind does not increase in strenght, continually increased in magnitude, rising higher and extending their bases, so as to in. clude a vast mass of water in each wave, which in its motion acts with great violence.
But if there be a mutual repulsion between the particles of oil, and no attraction between oil and water, oil dropped on water will not be held together by adhesion to the spot whereon it falls; it will not be imbibed by the water; it will be at liberty to expand itself: and it will spread on a surface that, besides being smooth to the most perfect degree of polish, prevents, perhaps by repelling the oil, all immediate contact, keeping it at a minute distance from itself; and the expansion will continue till the mutual repulsion between the particles of the oil is weakened and reduced to nothing by their distance.
Now I imagine that the wind, blowing over water thus covered with a film of oil, cannot 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.
Totally therefore we might suppress the waves in any required place, if we could come at the windward place
where they take their rise. This in the ocean can seldom if ever be done. But perhaps something may be done on particular occasions, to moderate the violence of the waves when we are in the midst of them, and prevent their breaking where that would be inconvenient.
For when the wind blows fresh, there are continually rising on the back of every great wave a number of small ones, which roughen its surface, and give the wind hold, as it were, to push it with greater force. This hold is di. minished, by preventing the generation of those small ones. and possibly too, when a wave's surface is oiled, the wind, in passing over it, may rather in some degree press it down, and contribute to prevent it rising again, instead of promoting it.
This as mere conjecture would have little weight, if the appearent effects of pouring oil into the midst of waves were not considerable, and as yet not otherwise accounted for.
When the wind blows so fresh, as that the waves are not sufficiently quick in obeying its impulse, their tops, being thinner and lighter, are pushed forward, broken, and turned over in a white foam. Common waves lift a vessel without entering it; but these when large some. timies break above and pour over it, doing great damage.
That this effect might in any degree be prevented, or the height and violence of waves in the sea moderated, we had no certain account; Pliny's authority for the practice of seamen in his time being slighted. But discoursing lately on this subject with his excellency Count Bentinck, of Holland, his son the honourable Captain Bentinck, and the learned professor Allemand, (to all whom I showed the experiment of smoothing in a windy day the large piece of water at the head of the Green Park) a letter was mentioned, which had been received by the Count from Batavia, relative to the saving of a Dutch ship in a storm by pouring oil into the sea. I much desired to see that letter, and a copy of it was promised me, which I afterward received.
EXTRACT OF A LETTER ON THE
- Near the islands Paul and Amsterdam, we met with a storm, which had nothing particular in it worthy of being communicated to you, except that the captain found himself obliged for greater safety in wearing the ship, to pour oil into the sea, to prevent the waves breaking over her, which had an excellent effect, and succeeded in pre
serving iis. As he ponred out but a little at a time, the East India Company owes perhaps its ship to only six demiames of oil-olive. I was present upon deck when this was done; and I should not have mentioned this circumstance to you, but that we have found people here so prejudiced against the experiment, as to make it necessary for the officers on board and myself to give a certificate of the truth on this head, of which we made no difficulty.
On this occasion, I mentioned to Captain Bentinck, a thought which had occurred to me in reading the voyages of our late circumnavigators, particularly where accounts are given of pleasant and fertile islands which they much desired to land upon, when sickness made it more necessary, but could not effect a landing through a violent surf breaking on the shore, which rendered it impracticable. My idea was, that possibly by sailing to and fro at some distance from such lee-shore, continually pouring oil into the sea, the waves might be so much depressed, and lessened before they reached the shore, as to abate the height and violence of the surf, and permit a landing; which, in such circumstances, was a point of sufficient importance to justify the expense of the oil that miglit be requisite for the purpose. That gentleman, who is ever ready to promote what may be of public utility, though his own ingenious inventions have not always met with the countenance they merited, was so obliging as to invite me to Portsmouth, where an opportunity would probably offer, in the course of a few days, of making the experiment on some of the shores about Spithead, in which he kindly proposed to accompany me, and to give assistance with such boats as night be necessary. Accordingly, about the middle of October last, I went with some friends to Portsmouth; and a day of wind happening, which made a lee-shore between Haslar-hospital and the point near Jillkecker, we went from the Centaur with the long-boat and barge towards that shore. Our disposition was this: the long-boat was anchored about a quarter of a mile from the shore; part of the company were landed behind the point (a place more sheltered from the sea) who came round and placed themselves opposite to the longboat where they might observe the surf, and note if any change occurred in it upon using the oil. – Another party, in the barge, plied to windward of the long-boat, as far from her as she was from the shore, making trips of about half a mile each, pouring oil continually ont of a large stone-bottle, through a hole in the cork, somewhat bigger than a goose.quill. The experiment had not, in the main point, the success we wished, for no material difference was observed in the height or force of the surf upon the shore; but those who were in the long-boat conld observe a tract of smoothed water, the whole of the distance in which the barge poured the oil, and gradually spreading in breadth towards the long-boat. I call it smoothed, not
that it was laid level; but because, though the swell continued, its surface was not roughened by the wrinkles, or smaller
before-nientioned; and none or very few white caps (or waves whose tops turn over in foam) appeared in that whole space, though to windward and leeward of it there were plenty; and a wherry, that came round the point under sail, in her way to Portsmouth, seemed to turn into that tract of choice, and to use it froni end to end, as a piece of turnpike-road.
It may be of use to relate the circumstances of an experiment that does not succeed, since they may give hints of amendment in future trials: it is therefore I have been thus particular. I shall only add what I apprehend may have been the reason of our disappointment.
I conceive, that the operation of oil on water is, first, to prevent the raising of new waves by the wind and, secondly, to prevent its pushing those before raised with such force, and consequently their continuance of the same repeated height, as they would have done, if their surface were not oiled. — But oil will not prevent waves being raised by another power, by a stone, for instance, falling into a still pool; for they then rise by the mechanical impulse of the stone, which the greasiness on the surrounding water cannot lessen or prevent, as it can prevent the winds catching the surface and raising it into waves. Now waves once raised, whether by the wind or any other power, have the same mechanical operation, by which they continue to rise and fall, as a pendulum will continue to swing, a long time after the force ceases to act by which the motion was first produced: that motion will, however, cease in time; but time is necessary. There fore, though oil spread on an agitated sea may weaken the push of the wind on those waves whose surfaces are covered by it, and so, by receiving less fresh impulse, they may gradually subside; yet a considerable time, or a distance through which they will take time to move, may be necessary to make the effect sensible on any shore in a diminution of the surf: for we know, that when wind ceases suddenly, the waves it has raised do not as suddenly subside, but settle gradually, and are not quite down till after the wind has ceased. So though we should, by oiling them, take off the effect of wind on waves already raised, it is not to be expected that those waves should be instantly levelled. The motion they have received will, for some time, continue; and if the shore is not far distant, they arrive there so soon, that their effect upon it will not be visibly diminished. Possibly, therefore, if we had begun our operations at a greater distance, the effect miglit have been more sensible. And perhaps we did not pour oil in sufficient quantity. Future experimients way determine this.
I was, however, greatly obliged to Captain Bentinck, for the chearful and ready aids he gave me: and I ought not to omit mentioning Mr. Banks, Dr. Solander, General
Carnoc, and Dr. Blagden. who all assisted at the experiment, during that blustering unpleasant day, with a patience and activity that could only be inspired by a zeal for the improvement of knowledge, such especiaily as might possibly be of use to men in situations of distress.
I would wish you to communicate this to your ingenious friend, Mr. Farish, with my respects; and believe me to be, with sincere esteem,
FROM DR. BERKINS, OF BOSTON, TO
BENJAMIN FRANKLIN, ESQ.
Boston, Aug. 3, 1752. SIR, This comes to you on account of Dr. Douglas: he de. sired me to write to you for what you know of the number that died of the Inoculation in Philadelphia, telling me lie designed to write something on the small-pox shortly. We shall both be obliged to you for a word on this affair.
The chief particulars of our visitation, you have in the public prints. But the less degree of mortality than nsual in the common way of infection, seems chiefly owing to the purging method designed to prevent the secondary fever: a method first begun and carried on in this town, and with success beyond expectation. We lost one in eleven one-sixth, but had we been experienced in this way, at the first coming of the distemper, probably the proportion hat'leen but one in thirteen or fourteen.
In the year 1730 we lost one in nine, which is more favourablc than ever before with us. The distemper pretty much the same then as now, but some circumstances not so kind this time.
If there be any particulars which you want to know, please to signify what they are, and I shall send them.
The number of our inhabitants decreases. On a strict inquiry, the overseers of the poor find but fourteen thou. sand one hundred and ninety Whites, and one thousand five hundred and forty-four Blacks, including those absent, on account of the small-pox, many of whom, it is probable, will never return.