I received with the greatest pleasure, my illustrious doctor, the last two letters you did me the honor of writing, but I did not receive the first. I cannot tell you the joy I felt in learning that your health was holding up so well, and that it was even better there than it had been here. That seems to me to prove that in general, the more the body is in good health, the less pain is felt from particular causes, which fully confirms what the famous Hoffman says on this subject. M. de Buffon, who was having troubles similar to yours, and even worse, feels better when he is at home in Montbard.

You never waste time, my illustrious doctor; it is a truly admirable thing to see you cross the seas at your age, risking upsetting pains and yet always keeping your head and spirit so calm that you are able to apply yourself to those things which interest you. I shall be enchanted to see your memoirs on the different stoves which you mentioned to me, as well as your research on navigation. My brother, to whom I sent your letter, was most flattered to see that you did not forget him, and that you kindly sent him your maritime research. I believe he must have told you this.

Since your departure, there have been several balloon experiments as you will have been able to learn from the newspapers. Doubtless you heard about the fatal catastrophe of the unfortunate Pilatre de Rozier before you left. Blanchard is still making perilous ascents; he narrowly escaped disaster at the end of last year, but he lives (?) for the advancement of the art. However, it seems quite certain that he has so perfected the parachute, that he can drop animals in all safety from a very high altitude without them suffering the least harm; but he has not given us any information about the construction of these parachutes in terms of the surface area or their arrangement which could make us well informed and capable of making similar ones. Recently a very young man named Têtu conducted a balloon experiment in which he remained in the air for eleven hours, having gone up at five o'clock in the afternoon and not coming down again until the next day at four in the morning. As there wasn't any considerable wind, he did not go very far, but he assured us in the Academy, as he has already published, that around eleven o'clock he found himself in the midst of clouds where he experienced a considerable storm with violent thunderbolts. He repeated to us several times that he watched lightning flashes continuously around him and that he heard the thunder rumble below. Then he showed us a little flag with a hole in it, which he assured us had been made by a lightning bolt; it is true that the edges of it seemed to be blackened. He added further that, believing himself in an electrical storm, he extended a pointed rod near the edge of his basket and he saw a luminous point on it at times, and at others a beautiful heron's tuft. He observed the first phenomenon when he was in a raincloud, and the second when he was climbing higher in a snowcloud. He insisted that he saw this phenomenon several times, his balloon having been carried about, he said, in a kind of whirlwind, from the lower clouds to the higher ones, and then brought back from these to the lower clouds. He is going to start a second experiment. His thermometer went down to 5° below freezing.

The people from Javelle, whose activities you saw so often from your windows, conducted multiple experiments last autumn, or in 1785, from which it seems certain that they can climb and descend at will using their oars, without throwing out ballast, and without losing flammable air, which confirms what I have always thought, in opposition to M. Meusnier: it is sufficient to achieve a precarious equilibrium in the air, in order to perform any number of maneuvers, climbing, descending, etc., and it is up to the person in the balloon to achieve the degree of elevation that he wishes. What is certain is that Mme. Le Roy and Mesdames de Montalembert were in a free balloon last autumn, which went from Javelle to Issy, at a height of about 400 [feet], from which they came down; the weather was calm and they made the descent without difficulty. As for the Academy, they have done nothing more than ordering a 9-foot diameter balloon in order to see if its envelope would hold the air well, as you said in the past; it remained almost an entire year in the middle of the Academy without having lost enough of its flammable air to fall. It seems that this part of balloon fabrication is perfectly understood, and there is no longer the slightest difficulty in making them keep their flammable air. M. Meusnier has completed a treatise on the construction of balloons, an enormous piece of work which is truly invaluable and on which he worked very hard. For this project, he conducted some very interesting experiments on the resistance of different fabrics, and he solved several interesting problems about the form that these balloons should have in order to encounter the least resistance while conserving enough capacity. In his book, he gives the description and the dimensions of a very large balloon capable of carrying 24 people, where he insists on everything to which one needs to pay attention in constructing balloons. But carried away by his fluency, he does not seem attentive enough to the effectual element, I mean, the way of guiding it or propelling it. His methods are very imperfect, at least in my view, and absolutely incapable of producing any considerable effect. I would like to be able to clearly describe to you the disposition and play of his oars but in order to do this, I would require a whole volume, even without figures, and I still don't think I would be able to succeed. It seems that until now we were not on the path of trying anything which would have some success. However, I don't know if I am flattering myself, but I believe that I have found a shape for a balloon and an oar construction capable of producing results quite different and much superior to those which we have obtained up to this point. I am planning, my illustrious doctor, to have the honor of consulting you about this, you who know so well how to grasp the point of difficulty in these things, and how to find simple ways of resolving it. But I am putting off this conversation until another time, as this letter is already so long.

The lightning rods are causing a sensation. The Salle de la Comédie in Brest, where I had one installed, was visibly saved from a violent thunderbolt which struck the hall during the night of last June 15. The point of the rod was bent, and very clear marks of the bolt could be seen on the tip. On the 14th of the same month, the church of St. Philibert in Dijon was saved by its lightning rod from the effects of a furious lightning bolt which struck overhead. For, even though the bolt was seen heading towards the pointed rod with great speed, every part of the church was examined afterwards, and not the least sign of damage was found anywhere. However, something very curious was observed: the people who were inside the church swear that they saw a great deal of flashes at the time of the lightning bolt, and these people experienced or felt something like a lash from a whip on their legs; the same things was felt by a bell ringer who was in the belfry. I leave it to your usual wisdom to explain how this occurred.

I don't know if you know that the English are going to construct M. Huyghens' objective lens, the focal length of which is 200 feet. They want to use it to build aerial telescopes to compare their effects with those of M. Hirschel's [Herschel] reflecting telescopes.

Our chemists are still quite occupied with the decomposition of water, but if it occurs in nature's own combinations, as it surely does, this decomposition should result in various products which will require much time and wisdom to succeed in disentangling and identifying.

The fire machines are spreading here. They are going to build one near the Invalides, at the site called Gros Caillou. The day before yesterday, they laid the first stone of the building where it is to be built. This was done with a great deal of ceremony. The provost of merchants, who laid this first stone, was there with all of the city officials.

Adieu, my illustrious doctor. I must leave you, for fear that my letter will not leave. Please accept the sincere assurances of all the sentiments of attachment that I have devoted to you for life, and my wishes for your good health.