air's moving in every part as fast as the earth or sea it covers.
He that sails, or rides, has insensibly the same degree of motion as
the ship or coach with which he is connected. If the ship strikes
the shore, or the coach stops suddenly, the motion continuing in the
man, he is thrown forward. If a man were to jump from the land into
a swift sailing ship, he would be thrown backward (or towards the
stern) not having at first the motion of the ship.
He that travels by sea or land, towards the equinoctial, gradually
acquires motion; from it, loses.
But if a man were taken up from latitude 40 (where suppose the
earth's surface to move twelve miles per minute) and immediately set
down at the equinoctial, without changing the motion he had, his
heels would be struck up, he would fall westward. If taken up from
the equinoctial, and set down in latitude 40, he would fall eastward.
The air under the equator, and between the tropics, being constantly
heated and rarefied by the sun, rises. Its place is supplied by air
from northern and southern latitudes, which coming from parts where
the earth and air had less motion, and not suddenly acquiring the
quicker motion of the equatorial earth, appears an east wind blowing
westward; the earth moving from west to east, and slipping under the
Thus, when we ride in a calm, it seems a wind against us: if we ride
with the wind, and faster, even that will seem a small wind against
The air rarefied between the tropics, and rising, must flow in the
higher region north and south. Before it rose, it had acquired the
greatest motion the earth's rotation could give it. It retains some
degree of this motion, and descending in higher latitudes, where the
earth's motion is less, will appear a westerly wind, yet tending
towards the equatorial parts, to supply the vacancy occasioned by
the air of the lower regions flowing thitherwards.
Hence our general cold winds are about north west, our summer cold
gusts the same.
The air in sultry weather, though not cloudy, has a kind of haziness
in it, which makes objects at a distance appear dull and indistinct.
This haziness is occasioned by the great quantity of moisture equally
diffused in that air. 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.
Extreme cold winds congeal the surface of the earth, by
The five letters which I have the honor to present were written to Sir Joseph Banks, President of the Royal Society of London, in 1783, when Franklin was Minister to the Court of France and, with the collateral documents, they give perhaps the most complete and accurate account of the beginning of aerial navigation, enlivened with the humor and speculation characteristic of the writer.Page 1
 Complete Works of Benjamin Franklin, compiled and edited by John Bigelow, Volume VIII, New York, 1888.Page 2
I am told it is constructed of Linen & Paper, and is to be filled with a different Air, not yet made Public, but cheaper than that produc'd by the Oil of Vitriol, of which 200 Paris Pints were consum'd in filling the other.Page 3
One has ordered four of 15 feet Diameter each; I know not with what Purpose; But such is the present Enthusiasm for promoting and improving this Discovery, that probably we shall soon make considerable Progress in the art of constructing and using the Machines.Page 4
The Basket contained a sheep, a duck, and a Cock, who, except the Cock, received no hurt by the fall.Page 5
Faujas de St.Page 6
in passing thro' this Flame rose in the Balloon, swell'd out its sides, and fill'd it.Page 7
There is room in this Car for a little Table to be placed between them, on which they can write and keep their Journal, that is take Notes of every thing they observe, the State of their Thermometer, Barometer, Hygrometer, &c which they will have more Leisure to do than the others, having no fire to take Care of.Page 8
These Machines must always be subject to be driven by the Winds.Page 9
Some Guns were fired to give Notice, that the Departure of the.Page 10
great Balloon was near, and a small one was discharg'd which went to an amazing Height, there being but little Wind to make it deviate from its perpendicular Course, and at length the Sight of it was lost.Page 11
Tuesday Evening.Page 12
faire encore quelques observations, impatiente de la Lenteur de cette operation, a repris son Vol a 4 heures et 1/4, avec un excedant de Legerete d'environ 100 Livres par une Ascension droite et une rapidite telle qu'en peu de tems le Globe s'est trouve hors de vue.Page 13
Neither Bigelow nor Smyth print this document, which was first reproduced in the book mentioned by Franklin in the first paragraph of his letter, viz: "Description des Experiences de la Machine Aerostatique par M.Page 14
2d" corrected to "Sept.