The north-east winds of this country consist of regions of air from the north, travelling sometimes at the rate of about a mile in two minutes during the vernal months for several weeks together from the polar regions toward the south, the mercury in the barometer standing above 30. These winds consist of air greatly cooled by the evaporation of the ice and snow over which it passes, and as they become warmer by their contact with the earth of this climate are capable of dissolving more moisture as they pass along, and are thence attended with frosts in winter and with dry hot weather in summer.
1. This great quantity of air can not be supplied by superior currents passing in a contrary direction from south to north, because such currents must as they arise into the atmosphere a mile or two high become exposed to so great cold as to occasion them to deposit their moisture, which would fall through the inferior current upon the earth in some part of their passage.
2. The whole atmosphere must have increased in quantity, because it appears by the barometer that there exists one-fifteenth part more air over us for many weeks together, which could not be thus accumulated by difference of temperature in respect to heat, or by any aerostatic laws at present known, or by any lunar influence.
From whence it would appear that immense masses of air were set at liberty from their combinations with solid bodies, along with a sufficient quantity of combined heat, within the polar circle, or in some region to the north of us; and that they thus perpetually increase the quantity of the atmosphere; and that this is again at certain times re-absorbed, or enters into new combinations at the line or tropical regions. By which wonderful contrivance the atmosphere is perpetually renewed and rendered fit for the support of animal and vegetable life.
SOUTH-EAST WINDS.
The south-east winds of this country consist of air from the north which had passed by us, or over us, and before it had obtained the velocity of the earth's surface in this climate had been driven back, owing to a deficiency of air now commencing at the polar regions. Hence these are generally dry or freezing winds, and if they succeed north-east winds should prognosticate a change of wind from north-east to south-west; the barometer is generally about 30. They are sometimes attended with cloudy weather, or rain, owing to their having acquired an increased degree of warmth and moisture before they became retrograde; or to their being mixed with air from the south.
2. Sometimes these south-east winds consist of a vertical eddy of north- east air, without any mixture of south-west air; in that case the barometer continues above 30, and the weather is dry or frosty for four or five days together.
It should here be observed, that air being an elastic fluid must be more liable to eddies than water, and that these eddies must extend into cylinders or vortexes of greater diameter, and that if a vertical eddy of north-east air be of small diameter or has passed but a little way to the south of us before its return, it will not have gained the velocity of the earth's surface to the south of us, and will in consequence become a south-east wind.—But if the vertical eddy be of large diameter, or has passed much to the south of us, it will have acquired velocity from its friction with the earth's surface to the south of us, and will in consequence on its return become a south-west wind, producing great cold.
NORTH-WEST WINDS.
There seem to be three sources of the north-west winds of this hemisphere of the earth. 1. When a portion of southern air, which was passing over us, is driven back by accumulation of new air in the polar regions. In this case I suppose they are generally moist or rainy winds, with the barometer under 30, and if the wind had previously been in the south-west, it would seem to prognosticate a change to the north-east.