Benjamin Franklin: Experiments with Balloons, 1783

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Benjamin Franklin:

Experiments with Balloons, 1783

Although the Scientific Revolution was advanced most signally by a number of profound insights, it was the expansion of a "scientific mentality" which made it so culturally important. Here the famous American jack-of-all trade Benjamin Franklin (1706­1790) discusses in letters his experiments. . After he left Boston in 1723, he moved to Philadelphia, which he helped establish as one the centers of the Enlightenment in the American colonies. His work as an inventor (for instance his invention of a stove in 1742) and his theory on the identity of lightning and electricity, made him among the most famous of Americans in Europe.
These two letters, were written from France in 1783, at a time when Franklin was serving with the American diplomatic mission.


Passy, Dec. 1, 1783. Dear Sir:-

In mine of yesterday I promised to give you an account of Messrs. Charles & Robert's experiment, which was to have been made this day, and at which I intended to be present. Being a little indisposed, and the air cool, and the ground damp, I declined going into the garden of the Tuileries,2 where the balloon was placed, not knowing how long I might be obliged to wait there before it was ready to depart, and chose to stay in my carriage near the statue of Louis XV., from whence I could well see it rise, and have an extensive view of the region of air through which, as the wind sat, it was likely to pass. The morning was foggy, but about one o'clock the air became tolerably clear, to the great satisfaction of the spectators, who were infinite, notice having been given of the intended experiment several days before in the papers, so that all Paris was out, either about the Tuileries, on the quays and bridges, in the fields, the streets, at the windows, or on the tops of houses, besides the inhabitants of all the towns and villages of the environs. Never before was a philosophical experiment so magnificently attended. Some guns were fired to give notice that the departure of the balloon was near, and a small one was discharged, 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. Means were used, I am told, to prevent the great balloon's rising so high as might endanger its bursting. Several bags of sand were taken on board before the cord that held it down was cut, and the whole weight being then too much to be lifted, such a quantity was discharged as to permit its rising slowly. Thus it would sooner arrive at that region where it would be in equilibrio with the surrounding air, and by discharging more sand afterwards, it might go higher if desired. Between one and two o'clock, all eyes were gratified with seeing it rise majestically from among the trees, and ascend gradually above the buildings, a most beautiful spectacle. When it was about two hundred feet high, the brave adventurers held out and waved a little white pennant, on both sides their car, to salute the spectators, who returned loud claps of applause. The wind was very little, so that the object though moving to the northward, continued long in view; and it was a great while before the admiring people began to disperse. The persons embarked were Mr. Charles, professor of experimental philosophy, and a zealous promoter of that science; and one of the Messieurs Robert, the very ingenious constructors of the machine. When it arrived at its height, which I suppose might be three or four hundred toises, [A toise was a distance of about 2 meters] it appeared to have only horizontal motion. I had a pocket­glass, with which I followed it, till I lost sight first of the men, then of the car, and when I last saw the balloon, it appeared no bigger than a walnut. I write this at seven in the evening. What became of them is not yet known here. I hope they descended by daylight, so as to see and avoid falling among trees or on houses, and that the experiment was completed without any mischievous accident, which the novelty of it and the want of experience might well occasion. I am the more anxious for the event, because I am not well informed of the means provided for letting themselves down, and the loss of these very ingenious men would not only be a discouragement to the progress of the art, but be a sensible loss to science and society.
I shall inclose one of the tickets of admission, on which the globe was represented, as originally intended, but is altered by the pen to show its real state when it went off. When the tickets were engraved the car was to have been hung to the neck of the globe, as represented by a little drawing I have made in the corner.
I suppose it may have been an apprehension of danger in straining too much the balloon or tearing the silk, that induced the constructors to throw a net over it, fixed to a hoop which went round its middle, and to hang the car to that hoop.
Tuesday morning, December 2d.-I am relieved from my anxiety by hearing that the adventurers descended well near L'lsle Adam before sunset. This place is near seven leagues from Paris. Had the wind blown fresh they might have gone much farther.
If I receive any further particulars of importance, I shall communicate them hereafter.
With great esteem, I am, dear sir, your most obedient and most humble servant,

P.S. Tuesday evening.-Since writing the above I have received the printed paper and the manuscript containing some particulars of the experiment, which I enclose. I hear further that the travellers had perfect command of their carriage, descending as they pleased by letting some of the inflammable air escape, and rising again by discharging some sand; that they descended over a field so low as to talk with the labourers in passing, and mounted again to pass a hill. The little balloon falling at Vincennes shows that mounting higher it met with a current of air in a contrary direction, an observation that may be of use to future aerial voyagers.

From Nathan G. Coodman, ed. The Ingenious Dr. Franklin, Selected Scientific Letters of Benjamin Franklin (Philadelphia: t1niversity of Pennsylvania Press, 1931), pp. 99­105.


Passy,Jan. 16, 1784. Dear Friend,

I have this day received your favor of the 2d inst. Every information in my power, repecting the balloons, I sent you just before Christmas, contained in copies of my letters to Sir Joseph Banks. There is no secret in the affair, and I make no doubt that a person coming from you would easily obtain a sight of the different balloons of Montgolfier and Charles, with all the instructions wanted; and, if you undertake to make one, I think it extremely proper and necessary to send an ingenious man here for that purpose: otherwise, for want of attention to some particular circumstance, or of not being acquainted with it, the experiment might miscarry, which, in an affair of so much public expectation, would have bad consequences, draw upon you a great deal of censure, and affect your reputation. It is a serious thing to draw out from their affairs all the inhabitants of a great city and its environs, and a disappointment makes them angry. At Bordeaux lately a person who pretended to send up a balloon, and had received money from many people, not being able to make it rise, the populace were so exasperated that they pulled down his house, and had like to have killed him.

It appears, as you observe, to be a discovery of great importance, and what may possibly give a new turn to human affairs. Convincing sovereigns of the folly of wars may perhaps be one effect of it; since it will be impracticable for the most potent of them to guard his dominions. Five thousand balloons, capable of raising two men each, could not cost more than have ships of the line; and where is the prince who can afford so to cover his country with troops for its defence, as that ten thousand men descending from the clouds might not in many places do an infinite deal of mischief, before a force could be brought together to repel them? It is a pity that any national jealousy should, as you imagine it may, have prevented the English from prosecuting the experiment, since they are such ingenious mechanicians, that in their hands it might have made a more rapid progress towards perfection, and all the utility it is capable of affording.
The balloon of Messrs. Charles and Robert was really filled with inflamable air. The quantity being great, it was expensive, and tedious filling, requiring two or three days and nights constant labour. It had a soupape, [or valve], near the top, which they could open by pulling a string and thereby let out some air when they had a mind to descend; and they discharged some of their ballast of sand when they would rise again. A great deal of air must have been let out when they landed, so that the loose part might envelope one of them: yet, the car being lightned by that one getting out of it, there was enough left to carry up the other rapidly. They had no fire with them. That is only used in M. Montgolfier's globe, which is open at bottom, and straw constantly burnt to keep it up. This kind is sooner and cheaper filled; but must be much bigger to carry up the same weight; since air rarified by heat is only twice as light as common air, and inflamable air is ten times lighter. M. de Morveau, a famous chemist at Dijon, has found an inflamable air that will cost only a 25th part of the price of what is made by oil of vitriol [sulphuric acid] poured on iron filings. They say it is made from sea coal. Its comparative weight is not mentioned.

Yours most affectionately,


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