the East India Company owes perhaps its ship to only six demi-ames of oliveoil. 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 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 reach 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 might 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 might 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 Hasler 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 long-boat, 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 out 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 could 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 waves, before mentioned; 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 in preference, and to use it from 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. Therefore, 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 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 con

tinue; 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 might have been more sensible. And perhaps we did not pour oil in sufficient quantity. Future experiments may determine this.

I was, however, greatly obliged to captain Bentinck, for the cheerful and ready aids he gave me and I ought not to omit mentioning Mr. Banks, Dr. Solander, General Cardac, 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 especially 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, dear sir, your most obedient humble servant, B. FRANKLIN.

AN ATTEMPT TO EXPLAIN THE EFFECTS OF LIGHTNING, ON THE VANE OF THE STEEPLE OF A CHURCH IN CREMONA,

AUGUST, 1777.

TO DR. JOHN INGENHAUSZ.

1. When the subtile fluid which we call fire or heat enters a solid body, it separates the particles of which that body consists farther from each other, and thus dilates the body, increasing its dimensions.

2. A greater proportion of fire introduced separates the parts so far from each other that the solid body becomes a fluid being melted.

3. A still greater quantity of heat separates the parts so far, that they lose their mutual attraction, and acquire a mutual repulsion, whence they fly from each other, either gradually, or suddenly with great force, as the separating power is introduced gradually or suddenly.

4. Thus ice becomes water, and water vapor, which vapor is said to expand to 14,000 times the space it occupied in the form of water, and with an explosive force in certain cases capable of producing great and violent effects.

5. Thus metals expand, melt, and explode. The two first effected by the gradual application of the separating power, and all three, in its sudden application by artificial electricity, or lightning.

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6. That fluid in passing through a metal rod or wire is generally supposed to occupy the whole dimension of the rod. If the rod is smaller in some places than in others, the quantity of fluid which is not sufficient to make any change in the larger or thicker part, may be sufficient to expand, melt or explode the smaller, the quantity of fluid passing, being the same, and the quantity of matter less that is acted upon.

7. Thus the links of a brass chain, with a certain quantity of electricity passing through them have been melted in the small parts that form their contact, while the rest have not been affected.

8. Thus a piece of tin foil cut in this form, enclosed in a pack of cards,

and having the charge of a large bottle sent through it, has been found unchanged in the broadest part between a and b, melted only in spots between c and d, and the part between d and e reduced to smoke by explosion.

9. The tin foil melted in spots between b and c, and that whole space not being melted, seems to indicate that the foil in the melted parts had been thinner than the rest, on which thin parts the passing fluid had therefore a greater effect.

10. Some metals melt more easily than others. Tin more easily than copper, copper than iron. It is supposed (perhaps not yet proved) that those which melt with the least of the separating power, whether that be common fire or the electric fluid, do also explode with less of that power.

11. The explosions of metal like those of gun-powder act in all directions. Thus the explosion of gold leaf between plates of glass breaking the glass to pieces, will throw those pieces into all parts of the room, and the explosion of iron or even of water between the joints of stone in a steeple, will scatter the stones in all directions round the neighborhood. But the directions given to those stones by the explosion, is to be considered as different from the direction of the lightning which happened to occasion those explosions of the matter it ́met with in its passage between the clouds and the earth.

12. When bodies positively electrised approach sharp pointed rods or thin plates of metal, these are more easily rendered negative by the repulsive force

of the electric fluid in those positively electrised bodies, which chases away the natural quantity contained in those mince rods or plates, though it would not have force enough to chase the same out of larger masses. Hence such points, rods and plates being in a negative state, draw to themselves more strongly and in greater quantities the electric fluid offered them, than such masses can do which remain nearly in their natural state. And thus a pointed rod receives not only at its point though more visibly there, but at all parts of its length that are exposed. Hence a needle held between the finger and thumb, and presented to a charged prime conductor, will draw off the charge more expeditiously if held near the eye, and the rest of its length is exposed to the electrical atmosphere, than if all but half an inch of the point is concealed and covered.

13. Lightning so differs from solid projectiles, and from common fluids projected with violence, that though its course is rapid, it is most easily turned to follow the direction of good conductors. And it is doubted whether any experiments in electricity have yet decisively proved, that the electric fluid in its violent passage through the air where a battery is discharged has what we call a momentum, which would make it continue its course in a right line, though a conductor offered near that course to give it a different, or even contrary direction; or that it has a force capable of pushing forward, or overthrowing the objects it strikes against, even though it sometimes pierces them. Does not this seem to indicate that the perforation is not made by the force of a projectile passing through, but rather by the explosion or the dilatation in passing, of a subtile line of fluid?

14. Such an explosion or dilatation of a line of fluid passing through a card, would raise burrs round the hole sometimes on one side, sometimes on the other, and sometimes on both, according to the disposition of the part of the paper near the surface, without any regard to the direction of the fluid.

15. Great thanks are due to the ingenious philosopher who examined the vane at Cremona, and who took the pains to describe so exactly the effects of the lightning upon it, and to communicate that description. The fact is extremely curious. It is well worth considering. He invites to that consideration. He has fairly given his own opinion. He will with candor receive that of others, though it may happen to differ from his own. By calmly discussing rather than by warmly disputing, the truth is most easily obtained. I shall give my opinion freely, as it is asked, hoping it may prove the true one;