Winds. Days. Winds. Mr.
South-west . 112 South-east 32 North-west .. 58 East 26 North-west .. 50 South 18 West 53 North 16 The same resister shews, that the south-west wind blows more upon an average in each month of the year than any other, particularly in July and Au gust ; that the north-east prevails during January, March, April, May, and June, and is most unfrequent in February, July, September, and December; the north west occurring more frequently from November to March, and leas so in Sep tember and October than in any other months. In the fifth volume of the Sta tistical Account of Scotland there is a table of seven years close observation, made by Dr. Meek, near Glasgow, the average of which is stated as follows : Winds. Dave. Winds. Days.
South-west .. 174 North-east . 104 North-west .. 40 South-east . 47 In Ireland the prevailing winds are the west and south-west. The different de grees of its motion next excites our at tention ; and it seems almost superfluous to observe, that it varies in gradations from the gentlest zephyr, which plays upon the leaves of plants, gently undu. lating them, to the furious tempest, cal culated to inspire horror in the breast of the most callous ; it is also a most re markable fact, that violent currents of air pass along, as it were within a line, without sensibly agitating that beyond them. An instance of this kind occurred at Edinburgh, when the celebrated aero naut Lunardi ascended in his balloon, which was conveyed with great velocity by the wind, at the rate of 70 miles an hour, while a perfect calm existed in the city and neighbourhood.
There are many circumstances attend ing the operations of the air, which we term wind, that serve for a basis for well founded conjectures, and those united to the results of daily observation render the explanation of its phenomena tolera bly satisfactory. It must be clear to the most common capacity, that as the rays of the sun descend perpendicularly on the surface of the earth under the torrid zone, that part of it must receive a greater portion of heat than those where they fall Obliquely ; the heat thus acquired corn mumcates to the air, which it rarefies and causes to ascend,and the vacuum occasion ed by this operation, is immediately filled by the chill air from the north and south. The diurnal motion of the earth gradual ly lessens to the poles from the equator: at that point it moves at the rate of fif teen geographical miles in a minute : this motion is communicated to the atmo sphere in the same degree ; therefore, if part of it was conveyed instantaneously from latitude 30°, it would not directly acquire the velocity of that at the equa tor, consequently the ridges of the earth must meet it, and give it the appearance of an east wind ; the effect is similar up on the cold air proceeding from the north and south, and this similarity must be ad mitted to extend to each place particular ly heated by the beams of the sun.
The moon being a large body, situated comparatively near the earth, is known to affect the atmosphere in its revolutions by the pressure of that upon the sea, so as to cause the flux and reflux of it, which we term tides ; it cannot, therefore, be doubted that some of the winds we ex perience are caused by her motion.
The regular motion of the atmosphere, known by the name of land and sea breezes, may be accounted for upon the above principle : the heated rarefied land air rises, and its place is supplied by the chill damp air from the surface of the sea ; that from the hills in the neighbourhood becoming cold and dense, in the course of the niglat,descends and presses uponthe comparatively lighter air over the sea, and hence the land breeze. Granting that
the attraction of the moon, and the diur nal movement of the sun, affects our at mosphere, there cannot be a doubt but a westward motion of the air must pre vail within the boundaries of the trade winds, the consequence of which is an easterly current on each side : from this then it proceeds that south-west winds are so frequent in the western parts of Eu rope, and over the Atlantic ocean Mr. Kirwan attributes our constant south-west winds, particularly during winter, to an opposite current prevailing between the coast of Malabar and the Moluccas at the same period: this, he adds, must be sup plied from regions close to the pole, " which must be recruited in its turn from the countries to the south of it in the western parts of our hemisphere." The variable winds cannot be so rea dily accounted for, yet it is evident that, though they seem the effect of caprici ous causes, they depend upon a regular system, arranged by the great author of nature. That accurate and successful ob server of part of his works, the celebrat ed Franklin, discovered in 1740, that winds originate at the precise point to wards which they blow. This philosopher had hoped to observe an eclipse of the moon at Philadelphia, but was prevented by a north-east storm, that commenced at seven in the evening. This he after wards found did not occur at Boston till eleven; and upon enquiry, he had reason to suppose it passed to the north-east at the rate of about 100 miles an hour The manner in which he accounts for this re trograde proceeding is so satisfactory,that we shall give it in own words, parti cularly as his assertions are supported by recent observations both in America and Scotland. He argued thus : " I suppose a long canal of water, stopped at the end by a gate. The water is at rest till the gate is opened ; then It begins to move out through the gate, and the water next the gate is first in motion, and moves on towards the gate ; and so on successively, till the water at the head of the canal is in motion, which is last of all. In this case all the water moves indeed towards the gate ; but the successive times of begin ning the motion are in the contrary way, viz. from the gate back to the head of the canal. Thus, to produce a north-east storm, I suppose some great rarefaction of the air in or near the Gulph of Mexi co ; the air rising thence has its place sup plied by the next more northern, cooler, and therefore denser and heavier air ; a successive current is formed, to which out coast and inland mountains give a north east direction." According to the obser vations made by Captain Cook, the north east winds prevail in the Northern Paci fic Ocean during the same spring months they do with us, from which fact it ap pears the cold air from America and the north of Europe flows at that season into the Pacific and Atlantic Oceans.
The remaining descriptions of winds may arise from a variety of causes. As the atmosphere has been ascertained to be composed of air, vapour, and carbo nic acid and water, it is well known these frequently change their wild form, and combine with different substances, and the reverse; consequently partial voids and accumulations must continually oc cur, which occasion winds of different degrees of violence, continuance, and of direction.