Supposing you may not have received intelligence to be relied on as to the reality and extent of the late discovery of traversing the air in ballons, and having lately perused a book in which every thing is brought together on that subject as low down as Decemb. last, I will give you a detail of it. I will state the several experiments, with the most interesting circumstances attending them, by way of table, which will give you a clearer view and in less compass.

They suppose the minimum of these ballons to be of 6. inches diameter. These are constructed of gold beater’s skin and filled with inflammeable air. This air produced from iron-filings, the vitriolic acid and distilled water is, in weight, to Atmospheric air as 7. to 43. on an average of the trials; and when produced from the filings of Zinc, the Marine acid and distilled water, is to the Atmospheric air as 5. to 53. or 1. to 10 ½. But Montgolfier’s air is half the weight of Atmospheric. This is produced by burning straw and wool. The straw must be dry and open, and the wool shred very fine, so that they may make a clear flame, with as little smoke as possible. 50. ℔ of straw and 5. ℔ of wool filled the ballons of Oct. 19. and Nov. 21. in five minutes. These ballons contained 60,000 cubic feet. No analysis of this air is given us. Monsr. de Saint-fond, the author of the book, gives us a very great and useless display of Mathematical learning, which certainly has as yet had very little to do with the discovery, and when he comes to the chemical investigations, which are interesting, he sais little. The ballons sometimes were torn by the pressure of the internal air being insufficiently counteracted in the higher regions of the Atmosphere. These rents were of 6. or 7.f. length. Yet the machine descended with a gentle equable motion and not with an accelerated one. By the trials at Versailles and the Champ de Mars it appears that they will go with a moderate wind 150. leagues in 24. hours. There are yet two principal desiderata. 1. The cheapest and easiest process of making the lightest inflammable air. 2. An envelopment which will be light, strong, impervious to the air and proof against rain. Supplies of gas are desireable too, without being obliged to carry fire with the machine: for in those in which men ascended there was a store of straw and wool laid in the gallery which surrounded the bottom of the ballon and in which the men stood, and a chaffing dish of 3 feet cube in which they burnt the materials to supply air. It is conjectured that these machines may be guided by oars and raised and depressed by having vessels wherein, by the aid of pumps, they can produce a vacuum or condensation of atmospheric air at will. They are, from some new circumstances, strengthened in the opinion that there are generally opposite or different currents in the Atmosphere; and that if the current next the earth is not in the direction which suits you, by ascending higher you may find one that does. Between these there is probably a region of eddy where you may be stationary, if philosophical experiments be your object. The uses of this discovery are suggested to be 1. transportation of commodities under some circumstances; 2. traversing deserts, countries possessed by an enemy, or ravaged by infectious disorders, pathless and inaccessible mountains; 3. conveying intelligence into a beseiged place, or perhaps enterprizing on it, reconnoitring an army, &c.; 4. throwing new lights on the thermometer, barometer, hygrometer, rain, snow, hail, wind and other phaenomena of which the Atmosphere is the theatre; 5. the discovery of the pole, which is but one day’s journey, in a baloon, from where the ice has hitherto stopped adventurers; 6. raising weights, lightening ships over bars; 7. housebreaking, smuggling, &c. Some of these objects are ludicrous, others serious, important and probable. I will give you the figures of the baloons on the last page.

Congress has determined to adjourn on the 3d. of June to meet in November at Trenton. A vessel arrived here yesterday which left London the 25th. of March. She brings papers to the 20th. of that month. Mr. Pitt was still in place, supported by the city of London, the nation in general, and the House of Lords. Still however the majority in the House of commons was against him, tho reduced to 12. It was thought the parliament would be dissolved.

Be so good as to present my dutiful respects to my uncle and aunt and to be assured of the esteem with which I am Dr. Sir Your friend & servt,