COMETS. 



407 



low as 68, 67, 65, and even 57. Besides all 

 this, there was one very remarkable quality in the 

 fog or smoke of 1783 ; it appeared to possess a 

 phosphoric property, a light of its own. I find, at 

 least in the accounts of some observers, that it 

 afforded, even at midnight, a light which they com- 

 pare to that of the full moon, and which was suffi- 

 cient to enable one to see objects distinctly at a 

 distance of two hundred yards. To remove all 

 doubts as to the source of this light, it is recorded 

 that at the time there was a new moon. Such is 

 the state of the facts ; let us now see whether, in 

 order to explain them, it will be necessary to ad- 

 mit, that in 1783 the earth was immersed in the 

 tail of a comet. 



" The fog of 1783 was neither so constant, nor so 

 thick, as to prevent the stars being seen every 

 night, in all the places where it occurred. Ad- 

 mitting therefore that the earth was in the tail of 

 a comet, there is but one way of explaining why 

 the head of that comet was never seen, and this is, 

 by supposing, that it rose and set almost at the 

 same time with the sun ; that the superior light of 

 that luminary rendered it invisible; and that this 

 conjunction of the sun and comet lasted more than 

 a month. At a time when the proper motions of 

 comets appeared subject to no rule, when every 

 one disposed of them as he pleased, considering 

 them as mere meteors, the supposition we have 

 just made might be admitted ; but now that comets 

 are known to all astronomers to be heavenly bodies, 

 as obedient as the planets to the laws of Kepler ; 

 now that the mutual dependence of distance and 

 velocity is known ; now that observation and theory 

 combine to prove that all these bodies necessarily 

 move in their orbits with a rapidity that increases 

 as they approach the sun, it would be contrary to 

 all established principles to admit that a comet, 

 interposed between the sun and earth, could re- 

 volve about the sun in such a manner as to appear 

 constantly near it for more than a month, to a 

 spectator on the earth ! It is in vain to attempt to 

 explain the difficulty attending an exact conjunc- 

 tion, by supposing the tail very large. If it were 

 as large as that of 1744, the objection would re- 

 main in all its force. The dry fog of 1783, then, 

 whatever may have been said of it, was not the 

 tail of a comet." 



A dry fog, similar to the one above described, 

 was noticed in different quarters of the globe, in 

 1831. It was observed on the coast of Africa on 

 the 3d of August, in the south of France on the 

 10th, and at New York on the 15th of the same 

 month. This fog was so thick, that the sun might 

 be looked at all day, without any coloured glass or 

 other protection to the eye ; and, in some places, 

 the sun remained invisible till it had risen 15 or 

 20 above the horizon. When clearly seen, it was 

 often remarked, that the colour was changed to an 

 iizure blue, and sometimes to greenish or emerald 

 green. At night the heavens occasionally became 

 clear, so that the stars could be seen. Where this 

 fog was observed and while it continued, there was 

 a very unusual degree of light during the night. 

 In Siberia, at Berlin, and at Genoa, in the month 

 of August, the smallest writing could sometimes 

 be read even at midnight. This phenomenon, how- 

 ever, was not general, even in Europe. At Paris 

 and some other places, it was but faintly perceived, 

 and for a few days only. If a comet, therefore, 

 had passed at this time, between us and the sun, 

 no reason can be given why it was not seen. We 



are hence obliged to conclude, as in the former 

 case, that the fog was not attributable to a comet. 



The following are the remarks of Arago upon 

 the agency which this extraordinary fog is supposed 

 by some persons to have had in the uncommon pes- 

 tilence which made its appearance in Europe, about 

 the same time. 



" Many authors have chosen to see some con- 

 nection between the extraordinary fog of 1831 and 

 the entrance of the cholera morbus into Europe. 

 This opinion reminds me of what an old English 

 traveller, Matthew Dobson, says of the effects of 

 a periodical wind on the west coast of the continent 

 of Africa, which is called the Harmattan. On 

 reading over the original narrative just as I was 

 about to send these pages to the press, I was so 

 struck with several points of resemblance between 

 the properties of the air, where this wind prevails, 

 and that which is filled by the dry fogs of Europe, 

 that I determined to give here a short analysis of 

 that memoir. The reader will observe, that out 

 at sea, some distance from the shore, the Harmat- 

 tan loses its peculiar qualities ; and he will remem- 

 ber, that in 1783 the dry fog was not perceived in. 

 the middle of the Atlantic, although it darkened at 

 the same time the atmosphere of Europe and 

 America. He will see also, that all fogs of this 

 description are not fatal. A wind that blows three 

 times each season from the interior of Africa to 

 the Atlantic Ocean, is called the Harmattan. On 

 that part of the coast which lies between Cape 

 Verd (lat. 15 N.) and Cape Lopez (lat. 1 S.), 

 the Harmattan is chiefly felt in December, January, 

 and February. Its direction is between E.S.Eand 

 N.N.E. It commonly lasts two days, sometimes 

 five or six. It is always a moderate wind. A fog 

 of a particular kind, and thick enough to impede at 

 noon all but the red rays of the sun, always pre- 

 sents itself where the Harmattan blows. The par- 

 ticles, of which this fog is formed, are deposited on 

 the grass, on the leaves of trees, arid on the skin 

 of the negroes, in such profusion as to produce a 

 white appearance. Of the nature of these particles 

 we are ignorant ; we only know that the wind 

 carries them but a short distance from the shore. 

 A league out at sea the fog is much lighter ; and, 

 at the distance of three leagues, it disappears en- 

 tirely, although the Harmattan is still felt in all its 

 force. The extreme dryness of the Harmattan is 

 one of its most striking characteristics. When it 

 lasts some time, the branches of orange and citron 

 trees die ; the covers of books (even when they are 

 shut up in tight trunks, and have additional cover- 

 ing of linen,) warp as if they had been before a 

 large fire. Pannels of doors, window-shutters, and 

 articles of furniture crack and often break. The 

 effects of this wind upon the human body are not 

 less remarkable ; the eyes, lips, and palate become 

 dry and painful. If the Harmattan last four or 

 five days together, the skin of the hands and face 

 comes off; to prevent this, the natives rub their 

 bodies all over with grease. After what has been 

 said of the fatal effects of the Harmattan on vege- 

 tables, it may be thought that this wind must lie 

 very unhealthy, whereas quite the contrary is ob- 

 served. Intermittent fevers are completely cured 

 by the first breath of the Harmattan. Patients re- 

 duced by the excessive bleeding practised in that 

 country, recover their strength ; remittent and epi- 

 demic fevers also disappear, as if by enchantment. 

 Such is the salutary influence of this wind, that, 

 while it lasts, infection cannot be communicated 



