SIR, ON THE COMET SEEN IN YORKSHIRE, 1783. Passy, Dec. 15, 1783. All astronomical news that I receive, I think it my duty to communicate to you. The following is just come to hand, in a letter from the President of the Royal Society, dated at London the 9th instant. "A miserable comet made its appearance to Mr. Nathan Pigot, in his observatory at Yorkshire, on the 19th past, and the weather has been so hazy in the evenings that it has scarce been observed since. It was on the 19th "On the 21st it was seen in the place where it was expected; but the night was too hazy to observe it. "It appears like a nebula, with a diameter of about two minutes of a degree; the nucleus faint. It is seen with difficulty when the wires of the instrument are illuminated, but is not visible with an open glass."-Mr. Pigot. "Nov. 29th. It was seen near the chin of Aries, and appeared like a nebulous star: as there was some moon-light, it was difficult to find it, "Dec. 1st. It was removed near the preceding eye of Aries; but conceiving other astronomers who had fixed instruments, have noted its place, he has not calculated the distance from any known star."-Mr. Herschell. With great esteem, I have the honor to be, &c. B. FRANKLIN. ON BALLOONS, AND THEIR PROBABLE IMPORTANCE. TO DR. INGENHAUSZ. DEAR FRIEND, Passy, Jan. 16, 1784. I have this day received your favor of the 2d instant. Every information in my power respecting 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 Mongolfier 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 Bourdeaux 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 five 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 inflammable air. The quantity being great, it was expensive, and tedious filling, requiring two or three days and nights constant labor. 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 lightened 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 used only in M. Mongolfier'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 of much greater dimensions to carry up the same weight; since air rarefied by heat is only twice as light as common air, and inflammable air ten times lighter. Mons. Morveau, a famous chemist at Dijon, has discovered an inflammable air VOL. III. N that will cost only a 25th part of the price of what is made by oil of vitriol poured on iron filings. They say it is made from sea-coal. Its comparative weight is not mentioned. I am as ever, my dear friend, yours most affectionately, B. FRANKLIN. Passy, April 29, 1784. 20th instant. I thank you for I see your philosophers are in I received your kind letters of the 16th and your philosophical news. We have none here. the way of finding out at last what fire is. I have long been of opinion that it exists every where in the state of a subtile fluid. That too much of that fluid in our flesh gives us the sensation we call heat; too little, cold. Its vibrations, light. That all solid or fluid substances which are inflammable have been composed of it; their dissolution in returning to their original fluid state, we call fire. This subtile fluid is attracted by plants and animals in their growth, and consolidated. Is attracted by other substances, thermometers, &c. &c., variously; has a particular affinity with water, and will quit many other bodies to attach itself to water, and go off with it in evaporation. Adieu. Yours most sincerely, B. F. METEOROLOGICAL IMAGINATIONS AND CONJECTURES. May, 1784. THERE seems to be a region high in the air over all countries, where it is always winter, where frost exists continually; since in the midst of summer on the surface of the earth ice falls often from above, in the form of hail. Hail-stones of the great weight we sometimes find them, did not probably acquire their magnitude before they began to descend. The air being 400 times rarer than water, is unable to support it but in the shape of vapor, a state in which its particles are separated. As soon as they are condensed by the cold of the upper regions so as to form a drop, that drop begins to fall. If it freezes into a grain of ice, that ice descends. In descending, both the drop of water and the grain of ice are augmented by particles of the vapor they pass through in falling, and which they condense by their coldness, and attach to themselves. It is possible that in summer, much of what is rain when it arrives at the surface of the earth, might have been snow when it began its descent; but, being thawed in passing through the warm air near that surface, is changed from snow into rain. How immensely cold must be the original particle of hail, which forms the centre of the future hail-stone, since it is capable of communicating sufficient cold, if I may so speak,' to freeze all the mass of vapor condensed round it, and form a lump of perhaps six or eight ounces in weight! When in summer-time the sun is high, and long every day above the horizon, his rays strike the earth more directly and with longer continuance than in winter; hence the surface is more heated, and to a greater depth, by the effect of those rays. When rain falls on the heated earth, and soaks down into it, it carries down with it a great part of the heat, which by that means descends still deeper. The mass of earth, to the depth perhaps of 30 feet, being thus heated to a certain degree, continues to retain its heat for some time. Thus the first snows that fall in the beginning of winter, seldom lie long on the surface, but are soon melted and absorbed. After which the winds that blow over the country on which the snows had fallen, are not rendered so cold as they would have been by those snows, if they had remained. The earth, too, thus uncovered by the snow, which would have reflected the sun's rays, now absorbs them, receiving and retaining the warmth they afford. And thus the approach of the severity of winter is retarded; and the extreme degree of its cold is not always at the time we might expect it, viz. when the sun is at his greatest distance and the days the shortest, but some time after that period, according to the English proverb, which says, As the day lengthens, the causes of refrigeration continuing to operate, while the sun returns too slowly, and his force continues too weak, to counteract them. During several of the summer months of the year 1783, when the effect of the sun's rays to heat the earth in these northern regions should have been greatest, If I may so speak, because perhaps it is not by communicating cold to the particles of vapor that it freezes them, but by depriving them of their heat. there existed a constant fog over all Europe. This fog was of a permanent nature; it was dry, and the rays of the sun seemed to have little effect towards dissipating it, as they easily do a moist fog arising from water. They were indeed rendered so faint in passing through it, that when collected in the focus of a burning-glass they would scarce kindle brown paper; of course their summer effect in heating the earth was exceedingly diminished. Hence the surface was early frozen. Hence the first snows remained on it unmelted, and received continual additions. Hence the air was more chilled, and the winds more severely cold. Hence perhaps the winter of 1783-4 was more severe than any that had happened for many years. The cause of this universal fog is not yet ascertained. Whether it was adventitious to this earth, and merely a smoke proceeding from the consumption by fire of some of those great burning balls or globes which we happen to meet with in our rapid course round the sun, and which are sometimes seen to kindle and be destroyed in passing our atmosphere, and whose smoke might be attracted and retained by our earth; or, whether it was the vast quantity of smoke long continuing to issue during the summer from Hecla in Iceland, and that other volcano which arose out of the sea near that island, which smoke might be spread by various winds over the northern part of the world, is yet uncertain. It seems, however, worth the inquiry, whether other hard winters recorded in history, were preceded by similar permanent and widely-extended summer fogs. Because, if found to be so, men might from such fogs conjecture the probability of a succeeding hard winter, and of the damages to be expected by the breaking up of frozen rivers at the approach of spring, and take such measures as are possible and practicable to secure themselves and effects from the mischiefs that attended the last. PHYSICAL AND METEOROLOGICAL CONJECTURES, THE particles of air are kept at a distance from each other by their mutual repulsion. |