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that day was formed. From the averages of every day in the month, a general average was formed. The point from which the wind blew, was observed two or three times in every day. These observations, in the month of January, for instance, through the whole period, amounted to three hundred and thirty
At seventy-three of these, the wind was from the north ; forty-seven from the north-east, &c. So that it will be easy to see in what proportion each wind usually prevails in each month; or, taking the whole year, the total of observations through the whole period having been three thousand six hundred and ninetyeight, it will be observed that six hundred and eleven of them were from the north, five hundred and fifty-eight from the north-east, &c.
Though by this table it appears we have on an average fortyseven inches of rain annually, which is considerably more than usually falls in Europe, yet from the information I have collected, I suppose we have a much greater proportion of sunshine here than there. Perhaps it will be found, there are twice as many cloudy days in the middle parts of Europe, as in the United States of America. I mention the middle parts of Europe, because my information does not extend to its northern or southern parts.
In an extensive country, it will of course be expected that the climate is not the same in all its parts. It is remarkable, that proceeding on the same parallel of latitude westwardly, the
climate becomes colder in like manner as when you proceed north wardly. This continues to be the case till you attain the summit of the Alleghany, which is the highest land between the ocean and the Mississippi. From thence, descending in the same latitude to the Mississippi, the change reverses; and, if we may believe travellers, it becomes warmer there than it is in the same latitude on the sea-side. Their testimony is strengthened by the vegetables and animals which subsist and multiply there naturally, and do not on the sea-coast.
Thus Catalpas grow spontaneously on the Mississippi, as far as the latitude of 37°, and reeds as far as 38o. Parroquets even winter on the Scioto, in the 39th degree of latitude. In the summer of 1779, when the thermometer was at 90° at Monticello, and 96° at Williamsburg, it was 110° at Kaskaskia. 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 Alleghany, has not been ascertained ; but contemporary observations, made at Williamsburg, or in its neighborhood, 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 Williamsburg and the nearest mountains, at the position before mentioned, to be on an average 60 of Fahrenheit'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 height 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 five hundred feet perpendicular height above the river which washes its base. This position being nearly central between our nerthern and southern boundaries, and between the
bay and Alleghany, 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 Williamsburg, and at Monticello. It is formed by reducing nine months' observations at Monticello to four principal points, to wit, the north-east, 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, four hundred and twenty-one from the preceding table of winds at Williamsburg, 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 predominent wind at the mountains. The difference between these two winds to sensation, and in fact, is very great. The north-east is loaded with vapor, 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 south-eastern breezes come on generally in the afternoon. They have advanced into the country very sensibly within the memory of people now living. They formerly did not penetrate far above Williamsburg. 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 them, perhaps, go a little beyond it. They are of about twenty to thirty feet diameter horizontally. Of their height 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 volcanos, 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 autumn; 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 Williamsburg, the extremes 29 and 30.86 inches, the difference being 1.86 of an inch ; and in nine months, during which the height 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 Williamsburg, proved the variations in the weight of air to be simultaneous and corresponding in these two places.
Our changes from heat to cold, and cold to heat, are very sudden and great. The mercury in Fahrenheit's thermometer has been known to descend from 92° to 47° in thirteen hours.
It was 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 Williamsburg, in August 1766, the mercury in Fahrenheit's thermometer was at 98°, corresponding with 29. of Reaumur. At the same place in January 1780, it was 6o, corresponding with 11! below zero of Reau
I believe* these may be considered to be nearly the extremes of heat and cold in that part of the country. The latter may most certainly, as that time York river, at Yorktown, was frozen 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 Potomac. At Annapolis, where it is 5 miles over between the nearest points of land, the ice was from five to seven inches thick quite across, so that loaded carriages went over on it. Those, our extremes of heat and cold, of 6° and 98°, were indeed
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 Fahrenheit'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 135o above nothing. Late experiments show that the human body will exist in rooms heated to 140° of Reaumur, equal to 347° of Fahrenheit's, and 135° above boiling water. The hottest point of the twenty-four 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
* At Paris, in 1753, the mercury in Reaumur's thermometer was at 30% above zero, and in 1776, it was at 16 below zero. The extremities of heat and cold therefore at Paris, are greater than at Williamsburg, which is in the hottest part of Virginia.