QUERY VII
 
 

        _A notice of all what can increase the progress of human

knowledge?_
 
 

        Climate

        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 degree 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 neighbourhood, 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.
 
 

        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 point 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.
 
 

 

 

        Fall of Least & greatest

        rain, daily heat by                WINDS.

        &c. in Farenheit's

        inches thermometer.  N. N.E. E. S.E. S. S.W. W. N.W. Total.
 
 

 Jan.    3.192  38 1/2  to  44      73  47  32  10  11  78  40  46  337

 Feb.    2.049  41          47 1/2  61  52  24  11   4  63  30  31  276

 Mar.    3.95   48          54 1/2  49  44  38  28  14  83  29  33  318

 April   3.68   56          62 1/2  35  44  54  19   9  58  18  20  257

 May     2.871  63          70 1/2  27  36  62  23   7  74  32  20  281

 June    3.751  71 1/2      78 1/4  22  34  43  24  13  81  25  25  267

 July    4.497  77          82 1/2  41  44  75  15   7  95  32  19  328

 Aug.    9.153  76 1/4      81      43  52  40  30   9 103  27  30  334

 Sept.   4.761  69 1/2      74 1/4  70  60  51  18  10  81  18  37  345

 Oct.    3.633  61 1/4      66 1/2  52  77  64  15   6  56  23  34  327

 Nov.    2.617  47 3/4      53 1/2  74  21  20  14   9  63  35  58  294

 Dec.    2.877  43          48 3/4  64  37  18  16  10  91  42  56  334

 Total. 47.038  8.A.M.      4.P.M. 611 548 521 223 109 926 351 409 3698
 
 

 

        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 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 Missisipi.  From thence, descending in the same

latitude to the Missisipi, 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 Missisipi, as far as the latitude of

37 degrees. and reeds as far as 38 degrees.  Perroquets even winter on the

Sioto, in the 39th degree of latitude.  In the summer of 1779, when the

thermometer was at 90 degrees. at Monticello, and 96 at Williamsburgh, it was

110 degrees. at Kaskaskia.  Perhaps the mountain, which overhangs this

village on the North side, may, by its reflexion, have contributed somewhat

to produce this heat.  The difference of temperature of the air at the sea

coast, or on Chesapeak bay, and at the Alleghaney, has not been ascertained;

but cotemporary observations, made at Williamsburgh, or in its neighbourhood,

and at Monticello, which is on the most eastern ridge of 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 nearest

mountains, at the position before mentioned, to be on an average 6 1/8

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

degrees.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 1/37 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.  Williamsburgh 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 vapour, insomuch, that the salt makers have found that

their crystals would not shoot while that blows; it brings a

distressing chill, 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 in the 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 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 Williamsburgh, 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 has been

known to descend from 92 degrees. to 47degrees. in thirteen hours.
 
 

        It is taken for granted, that the preceding table of averaged

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 98degrees.  corresponding

with 29 1/3 of Reaumur.  At the same place in January 1780, it was at

6degrees.  corresponding with 11 1/2 below 0. of Reaumur.  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,

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 5 1/4 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 6degrees. and 98degrees. 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 58degrees. we are told, that the cold in

1735 sunk the mercury by Farenheit's scale to 126 degrees. 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 degrees. above nothing.

Late experiments shew that the human body will exist in rooms heated

to 140 degrees.  of Reaumur, equal to 347 degrees. of Farenheit, and

135 degrees.  above boiling water.  The hottest point of the 24 hours

is about four o'clock, P. M. and the dawn of day the coldest.
 
 

        (*) 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.
 
 

        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 degrees. have killed young plants of Indian

corn at 48 degrees. and have been known at 54 degrees.  Black frost,

and even ice, have been produced at 38 1/2 degrees.  which is 6 1/2

degrees above the freezing point.  That other circumstances must be

combined with the cold to produce frost, is evident from this also,

that 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 vapours, 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 no

instance of fruit killed by the frost in the neighbourhood 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 phaenomenon 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 a 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 knew an

instance, at York town, 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 phaenomenon as it shews itself at sea; but at

Monticello it is familiar.  There is a solitary mountain about 40

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 into 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 20

miles, and goes off to the South-west.  This phaenomenon begins to

shew 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 this 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 a sphere.