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tables and animals which subsist and multiply there naturally, and do not on our sea coast. Thus Catalpas grow spontaneously on the Mississippi, as far as the latitude of 37°, and reeds as far as 38°. Perroquets even winter on the Sciota, in the 39th degree of latitude. In the summer of 1779, when the thermometer was at 90° at Monticello, and 96 at Williamsburgh, it was 110° at Kaska ia. Perhaps the mountain, which overhangs this village on the north side, may, by its reflection, have contributed somewhat to produce this heat. The difference of temperature of the air at the sea coast, or on the Chesapeake bay, and at the Alleghaney, has not been ascertained ; but contemporary observations, made at Williamsburgh, or in its neighbourhood, and at Monticello, which is on the most eastern ridge of the mountains, called the South west, where they are intersected by the Rivanna, have furnished a ratio by which that difference may in some degree be conjectured. These observations make the difference between Williamsburgh and the mountains, at the position before mentioned, to be on an average 6°1-8 of Farenheit's thermometer. Some allowance, however, is to be made for the difference of latitude between these two places, the latter being 38° 8' 17'', which is 52' 22"' north of the former. By contemporary observations of between five and six weeks, the averaged and almost unvaried difference of the heighth of mercury in the barometer, at those two places, was .784 of an inch, the atmosphere at Monticello being so much the lightest, that is to say, about one thirty-seventh of its whole weight. It should be observed, however, that the hill of Monticello is of 500 feet perpendicular heighth above the river which washes its base. This position being nearly central between our northern and southern boundaries, and between the bay and Alleghaney, may be considered as furnishing the best average of the temperature of our climate. Williamsburg is much too near the south eastern corner to give a fair idea of our general temperature.
But a more remarkable difference is in the winds which prevail in the different parts of the country. The following table exhibits a comparative view of the winds prevailing at Williamsburgh, and at Monticello. It is formed by reducing nine months observations at Monticello to four principal points, to wit, the northeast, south-east, south-west, and north-west ; these points being perpendicular to, or parallel with our coast, mountains, and rivers: and by reducing in like manner, an equal number of observations, to wit, 421 from the preceding table of winds at Williamsburgh, taking them proportionably from every point.
By this it may be seen that the south-west wind prevails equally at both places; that the north-east is, next to this, the principal wind towards the sea-coast, and the north-west is the predominant wind at the mountains. The difference between these two winds to sensation, and in fact, is very great. The north-east is loaded with vapour, insomuch, that the salt makers have found that their crystals would not shoot while that blows; it brings a distressing chill, and is heavy and oppressive to the spirits: the north-west is dry, cooling, elastic and animating. The eastern and southeastern breezes come on generally in the afternoon. They have advanced into the country very sensibly within the memory of people now living. They forinerly did not penetrate far above Williamsburgh. They are now frequent at Richmond, and every now and then reach the mountains. They deposit most of their moisture however before they get that far. As the lands become more cleared, it is probable they will extend still further westward.
Going out into the open air, in the temperate, and warm months of the year, we often meet with bodies of warm air, which passing by us in two or three seconds, do not afford time to the most sensible thermometer to seize their temperature. Judging from my feelings only, I think they approach the ordinary heat of the human body. Some of themi perhaps go a little beyond it. They are of about 20 or 30 feet diameter horizontally. Of their heighth we have no experience, but probably they are globular volumes wafted or rolled along with the wind. But whence taken, where found, or how generated ? They are not to be ascribed to volcanoes, because we have none. They do not happen in the winter when the farmers kindle large fires in clearing up their grounds. They are not confined to the spring season, when we have fires which traverse whole counties, consuming the leaves which have fallen from the trees. And they are too frequent and general to be ascribed to accidental fires. I am persuaded their cause must be sought for in the atmosphere itself to aid us in which I know but of these constant circumstances; a dry air ; a temperature as warm at least as that of the spring or autumin; and a moderate current of wind. They are most frequent about sun set; rare in the middle parts of the day; and I do not recollect having ever met with them in the morning.
The variation in the weight of our atmosphere, as indicated by the barometer, is not equal to two inches of mercury. During twelve months observation at Williamsburgh, the extremes were 29, and 30.86 inches, the difference being 1.86 of an inch: and in nine. months, during which the heighth of the mercury was noted at Monticello, the extremes were 28.48 and 29.69 inches, the variation being 1.21 of an inch. A gentleman, who has observed his barometer many years, assures me it has never varied two inches. Contemporary observations, made at Monticello and Williamsburgh, proved the variations in the weight of air to be simula taneous and corresponding in these two places.
Our changes from heat to cold, and cold to heat, are
very sudden and great. The mercury in Farenheit's thermometer has been known to descend from 92° to 47° in thirteen hours.
It is taken for granted, that the preceding table of average heat will not give a false idea on this subject, as it proposes to state only the ordinary heat and cold of each month, and not those which are extraordinary. At Williamsburgh in August 1766, the mercury in Farenheit's therinometer was at 98° corresponding with 29} of Reaumur. At the same place in January 1780, it was 6o corresponding with 11} below 0, of Reaumur. I believe* these may be considered to be nearly the extremes of lieat and cold in that part of the country. The latter may most certainly, as at that time, York river, at York town, was frozey over, so that people walked across it; a circumstance which proves it to have been colder than the winter of 1740, 1741, usually called the cold winter, when York river did not freeze over at that place. In the same season of 1780, Chesapeake bay was solid, from its head to the mouth of Patowmac. At Annapolis, where it is 54 miles over between the nearest points of land, the ice was from 5 to 7 inches thick quite across, so that loaded carriages went over on it. Those, our extremes of heat and cold, of 6° and 98o were indeed very distressing to us, and were thought to put the extent of the human constitution to considerable trial. Yet a Siberian would have considered them as scarcely a sensible variation. At Jenniseitz in that country, in latitude 58° 27' we are told, that the cold in 1735 sunk the mercury by Farenheit's scale to 126° below nothing; and the inhabitants of the same country use stove rooms two or three times a week, in which they stay two hours at a time, the atmosphere of which raises the mercury to 135° above nothing. Late experiments show that the human body
* At Paris, in 1753, the mercury in Reaumur's thermometer was at 30 1-2 above 0, and in 1776, it was at 16 below 0. The extremities of heat and cold therefore at Paris, are greater than at Williamsburgh, which is in the hottest part of Virginia,
will exist in rooms heated to 140° of Reaumur, equal to 347° of Farenheit's, and 135° above boiling water.
The hottest point of the 24 hours is about four o'clock, P. M. and the dawn of day the coldest.
The access of frost in autumn, and its recess the spring, do not seem to depend merely on the degree of cold; much less on the air's being at the freezing point. White frosts are frequent when the thermometer is at 47°, have killed young plants of Indian corn at 48°, and have been known at 54o. Black frost, and even ice, have been produced at 381°, which is 63 degrees above the freezing point. That other circumstances must be combined with the cold to produce frost, is evident from this also, on the higher parts of mountains, where it is absolutely colder than in the plains on which they stand, frosts do not appear so early by a considerable space of time in autumn, and go off sooner in the spring, than in the plains. I have known frosts so severe as to kill the hiccory trees round about Monticello, and yet not injure the tender fruit blossoms then in bloom on the top and higher parts of the mountain; and in the course of 40 years, during which it had been settled, there have been but two instances of a general loss of fruit on it: while, in the circumjacent country, the fruit has escaped but twice in the last seven years. The plants of tobacco, which grow from the roots of those which have been cut off in the summer, are frequently green here at Christmas. This privilege against the frost is undoubtedly combined with the want of dew on the mountains. That the dew is very rare on their higher parts, I may say with certainty, from 12 years observations, having scarcely ever, during that time, seen an unequivocal proof of its existence on them at all during summer. Severe frosts in the depth of winter prove that the region of dews extends higher in that season than the tops of the mountains : but certainly, in the summer season, the vapours, by the time they attain that heighth, are become so attenuated as not to subside, and form a dew when the sun retires.