QUERY VII.



A NOTICE of all that can increaſe the progreſs of human knowledge?

Under the latitude of this query, I will preſume it not improper nor unacceptable to furniſh ſome data for eſtimating the climate of Virginia. Journals of obſervations on the quantity of rain, and degrees of heat, being lengthy, confuſed, and too minute to produce general and diſtinct ideas, I have taken five years' obſervations, to wit, from 1772 to 1777, made in Williamſburgh and its neighborhood, have reduced them to an average for every month in the year, and ſtated thoſe averages in the following table, adding an analytical view of the winds during the ſame period.

Fall of
rain,
&c., in
 inches. 
 Jan.   3.192
 Feb.   2.049
 March.   3.95
 April.   3.68
 May.   2.871
 June.   3.751
 July.   4.497
 Auguſt.    9.153
 Sept.   4.761
 Oct.   3.633
 Nov.   2.617
 Dec.   2.877
 Total.  47.038 
 Leaſt & greateſt 
daily heat
by Fahrenheit's
thermometer.
 38½  to  44
 41   47½
 48   54½
 56   62½
 63   70½
 71½   78¼
 77   82½
 76¼   81
 69½   74¼
 61¼   66½
 47¾   53½
 43   48¾
 8AM.   4PM.
 
WINDS.
 
N. N.E. E. S.E. S. S.W. W. N.W. Total
  73   47   32   10   11   78   40   46   337
  61   52   24   11    4   63   30   31   276
  49   44   38   28   14   83   29   33   318
  35   44   54   19    9   58   18   20   257
  27   36   62   23    7   74   32   20   281
  22   34   43   24   13   81   25   25   267
  41   44   75   15    7   95   32   19   328
  43   52   40   30    9  103   27   30   334
  70   60   51   18   10   81   18   37   345
  52   77   64   15    6   56   23   34   327
  74   21   20   14    9   63   35   58   294
  64   37   18   16   10   91   42   56   334
 611   548   521   223   109   926   351   409   3698 

The rains of every month, (as of January, for inſtance) through the whole period of years, were added ſeparately, and an average drawn from them. The cooleſt and warmeſt points of the ſame day in each year of the period, were added ſeparately, and an average of the greateſt cold and greateſt heat of that day, was formed. From the averages of every day in the month, a general average for the whole month 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 337. At 73 of theſe, the wind was from the north; at 47 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 3698, it will be obſerved that 611 of them were from the north, 558 from the north-eaſt, &c.

Though by this table it appears we have on an average 47 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 paralel of latitude weſtwardly, the climate becomes colder in like manner as when you proceed northwardly. This continues to be the caſe till you attain the ſummit of the Alleghaney, which is the higheſt land between the ocean and the Miſſiſippi. From thence, deſcending in the ſame latitude to the Miſſiſippi, 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 our ſea-coaſt. Thus catalpas grow ſpontaneouſly on the Miſſiſippi, as far as the latitude of 37°, and reeds as far as 38°. Perroquets 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 Cheſapeak bay, and at the Alleghaney, has not been aſcertained: but cotemporary obſervations, made at Williamſburgh, 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 61/8 degrees 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 cotemporary 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 500 feet perpendicular height 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 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, 421 from the preceding table of winds at Williamſburgh, taking them proportionably from every point.

 N.E.   S.E.   S.W.   N.W.   Total. 
 Williamſburgh   127  61  132  101  421
 Monticello  32 91 126 172 421

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 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 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 them perhaps go a little beyond it. They are of about 20 or 30 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 countries, 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 to 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 were 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. Cotemporary obſervations, made at Monticello and Williamſburgh, 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 Farenheit's thermometer his 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 thermometer was at 98° correſponding with 29 and one third of Reaumur. At the ſame place in January 1780, it was 6° correſponding with 11½ below 0, of Reaumur. I believe[1] 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 at that time, York River, at York town, 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, Cheſapeak bay was ſolid, from its head to the mouth of Patowmac. At Annapolis, where it is 5¼ 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 98° 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 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 in 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 54°. Black froſt, and even ice, have been produced at 38½°, which is 6½ 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 has 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 vapors, by the time they attain that height, are become ſo attenuated as not to ſubſide and form a dew when the ſun retires.

The weavil has not yet aſcended the high mountains.

A more ſatisfactory eſtimate of our climate to ſome, may perhaps be formed, by noting the plants which grow here, ſubject however to be killed by our ſevereſt colds. Theſe are the fig, pomegranate, artichoke, and European walnut. In mild winters, lettuce and endive require no ſhelter; but generally they need a ſlight covering. I do not know that the want of long moſs, reed, myrtle, ſwamp laurel, holly and cypreſs, in the upper country, proceeds from a greater degree of cold, nor that they were ever killed with any degree of cold in the lower country. The aloe lived in Williamſburgh, in the open air, through the ſevere winter of 1779, 1780.

A change in our climate, however, is taking place very ſenſibly. Both heats and colds are become much more moderate within the memory even of the middle-aged. Snows are leſs frequent and leſs deep. They do not often lie, below the mountains, more than one, two, or three days, and very rarely a week. They are remembered to have been formerly frequent, deep, and of long continuance. The elderly inform me, the earth uſed to be covered with ſnow about three months in every year. The rivers, which then ſeldom failed to freeze over in the courſe of the winter, ſcarcely ever do ſo now. This change has produced an unfortunate fluctuation between heat and cold, in the ſpring of the year, which is very fatal to fruits. From the year 1741 to 1769, an interval of twenty-eight years, there was an inſtance of fruit killed by the froſt in the neighborhood of Monticello. An intenſe cold, produced by conſtant ſnows, kept the buds locked up till the ſun could obtain, in the ſpring of the year, ſo fixed an aſcendency as to diſſolve thoſe ſnows, and protect the buds, during their developement, from every danger of returning cold. The accumulated ſnows of the winter remaining to be diſſolved all together in the ſpring, produced thoſe overflowings of our rivers, ſo frequent then, and ſo rare now.

Having had occaſion to mention the particular ſituation of Monticello for other purpoſes, I will juſt take notice that its elevation affords an opportunity of ſeeing a phænomenon which is rare at land, though frequent at ſea. The ſeamen call it looming. Philoſophy is as yet in the rear of the ſeamen, for ſo far from having accounted for it, ſhe has not given it name. Its principal effect is to make diſtant objects appear larger, in oppoſition to the general law of viſion, by which they are diminiſhed. I know an inſtance, at Yorktown, from whence the water proſpect eaſtwardly is without termination, wherein a canoe with three men, at a great diſtance was taken for a ſhip with its three maſts. I am little acquainted with the phenomenon as it ſhows itſelf at ſea; but at Monticello it is familiar. There is a ſolitary mountain about forty miles off in the ſouth, whoſe natural ſhape, as preſented to view there, is a regular cone; but, by the effect of looming, it ſometimes ſubſides almoſt totally in the horizon; ſometimes it riſes more acute and more elevated; ſometimes it is hemiſpherical; and ſometimes its ſides are perpendicular, its top flat, and as broad as its baſe. In ſhort it aſſumes at times the moſt whimſical ſhapes, and all theſe perhaps ſucceſſively in the ſame morning. The Blue ridge of mountains comes into view, in the north-eaſt, at about 100 miles diſtance, and approaching in a direct line, paſſes by within twenty miles, and goes off to the ſouth-weſt. This phænomenon begins to ſhow itſelf on theſe mountains, at about 50 miles diſtance and continues beyond that as far as they are ſeen. I remark no particular ſtate, either in the weight, moiſture, or heat of the atmoſphere, neceſſary to produce this. The only conſtant circumſtances are its appearance in the morning only, and on objects at leaſt 40 or 50 miles diſtant. In this latter circumſtance, if not in both, it differs from the looming on the water. Refraction will not account for the metamorphoſis. That only changes the proportions of length and breadth, baſe and altitude, preſerving the general outlines. Thus it may make a circle appear elliptical, raiſe or depreſs a cone, but by none of its laws, as yet developed, will it make a circle appear a ſquare, or a cone or a ſphere.



  1. At Paris, in 1753, the mercury in Reaumur's thermometer was at 30½ above 0, and in 1776, it was 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.