When by the cold wind blowing down among it, it is condensed into clouds and falls in rain, the air becomes purer and clearer hence after gusts, distant objects appear distinct, their figures sharply terminated.

up from

Extreme cold winds congeal the surface of the earth, by carrying off its fire. Warm winds afterwards blowing over that frozen surface, will be chilled by it. Could that frozen surface be turned under, and a warmer turned beneath it, these warm winds would not be chilled so much. The surface of the earth is also sometimes much heated by the sun; and such heated surface not being changed, heats the air that moves over it.

1

Seas, lakes, and great bodies of water agitated by the winds, continually change surfaces; the cold surface in winter is turned under by the rolling of the waves (and the air over it), and a warmer turned up: in summer the warm turned under, and cooler turned up. Hence the more equal temper of seawater, and the air over it. Hence in winter, winds from the sea seem warm, In summer the contrary.

winds from the land cold.

Therefore the lakes north-west of us,' as they are not so much frozen nor so apt to freeze as the earth, rather moderate than increase the coldness of our winter winds.

The air over the sea being warmer, and therefore lighter in winter than the air over the frozen land, may be another cause of our general north-west winds; which blow off to sea at right angles from our North-American coast. The warm light sea air rising, the heavy cold land air pressing into its place.

Heavy fluids descending, frequently form eddies or whirlpools, as is seen in a funnel, where the water acquires a circular motion, receding every way from a centre, and leaving a vacancy in the middle, greatest above, and lessening downwards, like a speaking trumpet, its biggest end upwards.

Air ascending or descending may form the same kind of eddies or whirlings, the parts of air acquiring a circular motion, and receding from the middle of the circle by a centrifugal force, and leaving there a vacancy, if descending, greatest above, and lessening downwards; if ascending, greatest below and lessening upwards, like a speaking trumpet standing its big end on the ground. When the air descends with violence in some places, it may rise with equal violence in others, and form both kinds of whirlwinds.

The air in its whirling motion receding every way from the centre or axis of

'In Pennslyvania.

the trumpet, leaves there a vacuum; which cannot be filled through the sides, the whirling air as an arch preventing; it must then press in at the open ends. The greatest pressure inwards must be at the lower end, the greatest weight of the surrounding atmosphere being there. The air entering rises within and carries up dust, leaves, and even heavier bodies that happen to be in its way, as the eddy or whirl passes over land.

If it passes over water, the weight of the surrounding atmosphere forces up the water into the vacuity, part of which by degrees joins with the whirling air, and adding weight and receiving accelerated motion, recedes still farther from the centre or axis of the trumpet as the pressure lessens, and at last is broken into small particles, and so united with air as to be supported by it, and become black clouds at the top of the trump.

Thus these eddies may be whirlwinds at land, water-spouts at sea. A body of water so raised may be suddenly let fall when the motion, &c. has not strength to support it, or the whirling arch is broken so as to let in the air. Falling in the sea, it is harmless, unless ships happen to be under it. But if in the progressive motion of the whirl it has moved from the sea over to the land, and there breaks; sudden, violent, and mischievous torrents are the consequence. B. FRANKLIN.

ON ELECTRICITY.

A THREE WHEELED CLOCK-GRAVITATION OF BODIES AFFECTED BY SUN AND MOON-CONJECTURE ON TIDES.

MY DEAR FRIEND,

To DR. INGENHAUSZ.

Passy, April 29, 1785.

I believe my last letter to you was of May 16, 1783. I am therefore much in your debt as a correspondent. I have now before me all your letters since received, and shall endeavor as well as I can to answer them. I confess that a man who can leave so many letters so long unanswered, does not deserve so valuable a correspondence as yours. But I am grown very old, being now in my eightieth year: I am engaged in much business that must not be neglected. Writing becomes more and more irksome to me: I grow more indolent: philosophic discussions, not being urgent like business, are postponed from time to time till they are forgotten; besides, I have been these twenty months past afflicted with the stone, which is always giving me more or less uneasiness, unless when I am laid in bed; and when I would write, it

interrupts my train of thinking, so that I lay down my pen, and seek some light

amusement.

I consent to your request concerning my paper on the weathercock struck by lightning. Dispose of it as you please.

You will find an account of the first great stroke I received, in pages 160, 161, of my book, 5th edition, 1774. The second I will now give you. I had a paralytic patient in my chamber, whose friends brought him to receive some electric shocks: I made them join hands so as to receive the shock at the same time, and I charged two large jars to give it. By the number of those people I was obliged to quit my usual standing, and placed myself inadvertently under an iron hook which hung from the ceiling down to within two

See WRITINGS, Part IV.

[Extract from the same.]

Turkey killed by electricity-Effect of a shock on the operator in making the experiment. As Mr. Franklin, in a former letter to Mr. Collinson, mentioned his intending to try the power of a very strong electrical shock upon a turkey, that gentleman accordingly has been so very obliging as to send an account of it, which is to the following purpose.

He made first several experiments on fowls, and found, that two large thin glass jars gilt, holding each about six gallons, were sufficient, when fully charged, to kill common hens outright; but the turkies, though thrown into violent convulsions, and then lying as dead for some minutes, would recover in less than a quarter of an hour. However, having added three other such to the former two, though not fully charged, he killed a turkey of about ten pounds weight, and believes that they would have killed a much larger. He conceited, as himself says, that the birds killed in this manner ate uncommonly tender.

In making these experiments, he found, that a man could, without great detriment, bear a much greater shock than he had imagined: for he inadvertently received the stroke of two of these jars through his arms and body, when they were very near fully charged. It seemed to him an universal blow throughout the body from head to foot, and was followed by a violent quick trembling in the trunk, which went off gradually, in a few seconds. It was some minutes before he could recollect his thoughts, so as to know what was the matter; for he did not see the flash, though his eye was on the spot of the prime conductor, from whence it struck the back of his hand; nor did he hear the crack, though the by-standers said it was a loud one; nor did he particularly feel the stroke on his hand, though he afterwards found it had raised a swelling there, of the bigness of half a pistolbullet. His arms and the back of the neck felt somewhat numbed the remainder of the evening, and his breast was sore for a week after, as if it had been bruised. From this experiment may be seen the danger, even under the greatest caution, to the operator, when making these experiments with large jars; for it is not to be doubted, that several of these fully charged would as certainly, by increasing them, in proportion to the size, kill a man, as they before did a turkey.

N. B. The original of this letter, which was read at the Royal Society, has been mislaid.

inches of my head, and communicated by wire with the outside of the jars. I attempted to discharge them, and in fact did so; but I did not perceive it, though the charge went through me, and not through the persons I intended it for. I neither saw the flash, heard the report, nor felt the stroke. When my senses returned, I found myself on the floor. I got up, not knowing how that had happened. I then again attempted to discharge the jars; but one of the company told me they were already discharged, which I could not at first believe, but on trial found it true. They told me they had not felt it, but they saw I was knocked down by it, which had greatly surprised them. On recollecting myself, and examining my situation, I found the case clear. A small swelling rose on the top of my head, which continued sore for some days; but I do not remember any other effect, good or bad. The stroke you received, and its consequences, are much more curious. I communicated that part of your letter to an operator, encouraged by government here to electrify epileptic and other poor patients, and advised his trying the practice on mad people according to your opinion. I have not heard whether he has done it.

I do not know that my contrivance of a clock with three wheels only, which showed hours, minutes, and seconds, has ever been published. I have seen several of them here at Paris that were made by Mr. Whitehurst, and sent over I believe by Mr. Magellan. You are welcome to do what you please with it. Mr. Whitehurst's invention is very simple, and should be very effectual, provided the foot of the rod and the situation of the clock are invariably fixed, so as never to be at a greater or less distance from one another, which may be by fixing both in a strait-grained piece of wood of about four feet long; wood not changing its dimensions the length-way of the grain, by any common degree of heat or cold. But this cannot be trusted to in the wood of a clock case, because in sawing boards the grain is frequently crossed, and moisture and dryness will change their dimensions.

You are at liberty also to publish, if you think fit, the experiment of the globe floating between two liquors. I suppose you remember to have seen it on my chimney-piece. Though it is a matter of no utility. Something of the same nature has been done more than an hundred years since by another person, I forget who.

What I formerly mentioned to you of hanging a weight on a spiral spring, to discover if bodies gravitated differently to the earth during the conjunctions of the sun and moon, compared with other times, was this. We suppose that by

the force of gravity in those luminaries, the water of the ocean, an immense weight, is elevated so as to form the tides: if that be so, might we not expect that an iron ball of a pound weight, suspended by a fine spiral spring, should, when the sun and moon are together both above it, be a little attracted upwards

or rendered lighter, so as to be drawn up a little by the spring on which it depends, and the contrary when they are both below it. The quantity, though very small, might perhaps be rendered visible by a contrivance like this in the margin. It is not difficult to make this experiment, but I have never made it. With regard to the tides, I doubt the opinion of there being but two high waters and two low waters existing at the same time on the globe. I rather think there are many, and those at the distance

of about one hundred leagues from each other. The tides found in the river Amazons seem to favor this opinion. Observations hereafter in the isles of the Pacific Ocean, may confirm or refute it.

If I were in a situation where I could be a little more master of my time, I would, as you desire, write my ideas on the subject of chimnies: they might, I think, be useful. For by what I see everywhere the subject seems too little understood, which occasions much inconvenience and fruitless expense. But besides being harassed by too much business, I am exposed to numberless visits, some of kindness and civility, many of mere idle curiosity, from strangers of America and of different parts of Europe, as well as the inhabitants of the provinces who come to Paris. These devour my hours, and break my attention, and at night I often find myself fatigued without having done any thing. Celebrity may for a while flatter one's vanity, but its effects are troublesome. I have begun to write two or three things, which I wish to finish before I die; but I sometimes doubt the possibility.

B. FRANKLIN.