give a north-east direction." According to the observations made by Captain Cook, the north-east winds prevail in the Northern Pacific Ocean during the same spring months they do with us, from which facts it appears the cold air from America and the north of Europe flows at that season into the Pacific and

Atlantic Oceans,

288. Other descriptions of winds may arise from a variety of causes The atmosphere has been ascer. tained to be composed of air, vapour, and carbonic acid and water; and as it is well known that these frequently change their aerial form, and combine with different substances, and the reverse, consequently partial winds and accumulations must continually occur, which occasion winds of different degrees of violence, continuance, and direction.

2389. The principal electrical phenomena of the atmosphere are thunder and lightning. 2390. Thunder is the noise occasioned by the explosion of a flash of lightning passing through the air: or it is that noise which is excited by a sudden explosion of electrical clouds, which are therefore called thunder-clouds.

2391. The rattling, in the noise of thunder, which makes it seem as if it passed through arches, is probably owing to the sound being excited among clouds hanging over one another, between which the agitated air passes irregularly.

22. The explosion, if high in the air and remote from us, will do no mischief, but when near, it may; and it has, in a thousand instances, destroyed trees, animals, &c. This proximity, or small distance, may be estimated nearly by the interval of time between seeing the flash of lightning and hearing the report of the thunder, reckoning the distance after the rate of 1142 feet to a second of time, or 34 seconds to the mile. Dr. Wallis observes, that commonly the difference between the two is about seven seconds, which, at the rate above-mentioned, gives the distance almost two miles: but sometimes it comes in a second or two, which argues the explosion very near to us, and even among us; and in such cases, the doctor assures us, he has sometimes foretold the mischiefs that happened.

2993. Season of thunder. Although in this country thunder may happen at any time of the year, yet the months of July and August are those in which it may almost certainly be expected. Its devastations are of very uncertain continuance; sometimes only a few peals will be heard at any particular place during the whole season; at other times the storm will return, at intervals of three or four days, for a month, six weeks, or even longer; not that we have violent thunder in this country directly vertical in any one place so frequently in any year, but in many seasons it will be perceptible that thunder-clouds are formed in the neighbourhood, even at these short intervals. Hence it appears, that during this particular period, there must be some natural cause operating for the production of this phenomenon, which does not take place at other times. This cannot be the mere heat of the weather, for we have often a long tract of hot weather without any thunder; and besides, though not common, thunder is sometimes heard in the winter also. As therefore the heat of the weather is common to the whole summer, whether there is thunder or not, we must look for the causes of it in those phenomena, whatever they are, which are peculiar to the months of July, August, and the beginning of September. Now it is generally observed, that from the month of April, an east or south-east wind generally takes place, and continues with little interruption till towards the end of June. At that time, sometimes sooner and sometimes later, a westerly wind takes place; but as the causes producing the east wind are not removed, the latter opposes the west wind with its whole force. At the place of meeting, there are naturally a most vehement pressure of the atmosphere, and friction of its parts against one another; a calm ensues, and the vapours brought by both winds begin to collect and form dark clouds, which can have little motion either way, because they are pressed almost equally on all sides. For the most part, however, the west wind prevails, and what little motion the clouds have is towards the east: whence, the common remark in this country, that "thunder-clouds move against the wind." But this is by no means universally true: for if the west wind happens to be excited by any temporary cause before the natural period when it should take place, the east wind will very frequently get the better of it; and the clouds, even although thunder is produced, will move westward. Yet in either case, the motion is so slow, that the most superficial observers cannot help taking notice of a considerable resistance in the atmosphere.

2394 Thunderbolts. When lightning acts with extraordinary violence, and breaks or shatters any thing, it is called a thunderbolt, which the vulgar, to fit it for such effects, suppose to be a hard body, and even a stone. But that we need not have recourse to a hard solid body to account for the effects commonly attributed to the thunderbolt, will be evident to any one who considers those of gunpowder, and the several chemical fulminating powders, but more especially the astonishing powers of electricity, when only collected and employed by human art, and much more when directed and exercised in the course of nature. When we consider the known effects of electrical explosions, and those produced by lightning, we shall be at no loss to account for the extraordinary operations vulgarly ascribed to thunderbolts. stones and bricks struck by lightning are often found in a vitrified state, we may reasonably suppose, with Beccaria, that some stones in the earth, having been struck in this manner, gave occasion to the vulgar opinion of the thunderbolt.

As

225. Thunder-clouds are those clouds which are in a state fit for producing lightning and thunder. The first appearance of a thunder-storm, which usually happens when there is little or no wind, is one dense cloud, or more, increasing very fast in size, and rising into the higher regions of the air. The lower surface is black, and nearly level; but the upper finely arched, and well defined. Many of these clouds often seem piled upon one another, all arched in the same manner; but they are continually uniting, swelling, and extending their arches. At the time of the rising of this cloud, the atmosphere is commonly full of a great many separate clouds, which are motionless, and of odd whimsical shapes; all these, upon the appearance of the thunder-cloud, draw towards it, and become more uniform in their shapes as they approach; till, coming very near the thunder-cloud, their limbs mutually stretch towards one another, and they immediately coalesce into one uniform mass. Sometimes the thunder-cloud will swell, and increase very fast, without the conjunction of any adscititious clouds; the vapours in the atmosphere forming theinselves into clouds whenever it passes. Some of the adscititious clouds appear like white fringes, at the skirts of the thunder-cloud, or under the body of it; but they keep continually growing darker and darker, as they approach to unite with it. When the thunder-cloud is grown to a great size, its lower surface is often ragged, particular parts being detached towards the earth, but still connected with the rest. Sometimes the lower surface swells into various large protuberances, bending uniformly downward; and sometimes one whole side of the cloud will have an inclination to the earth, and the extremity of it will nearly touch the ground. When the eye is under the thunder-cloud, after it is grown large and well formed, it is seen to sink lower, and to darken prodigiously; at the same time that a number of small adscititious clouds the origin of which can never be perceived) are seen in a rapid motion, driving about in very uncertain directions under it. While these clouds are agitated with the most rapid motions, the rain commonly falls in the greatest plenty; and if the agitation be exceedingly great, it cominonly hails.

2396. Lightning. While the thunder-cloud is swelling, and extending its branches over a large tract of country, the lightning is seen to dart from one part of it to another, and often to illuminate its whole mass. When the cloud has acquired a sufficient extent, the lightning strikes between the cloud and the earth, in two opposite places; the

longer this lightning continues, the less dense does the cloud become, and the less dark its appearance; till at length it breaks in different places, and shows a clear sky. Those thunder-clouds are said to be sometimes in a positive as well as a negative state of electricity. The electricity continues longer of the same kind, in proportion as the thunder-cloud is simple and uniform in its direction; but when the lightning changes its place, there commonly happens a change in the electricity of the atmosphere over which the clouds passed. It changes suddenly after a very violent flash of lightning; but gradually when the lightning is moderate, and the progress of the thunder-cloud slow.

2397 Lightning is an electrical explosion or phenomenon. Flashes of lightning are usually seen in broad and undefined masses; when their path appears angular or zigzag, they are reckoned most dangerous. They strike the highest and most pointed objects in preference to others, as hills, trees, spires, masts of ships, &c. ; so all pointed conductors receive and throw off the electric fluid more readily than those that are terminated by flat surfaces. Lightning is observed to take and follow the readiest and best conductor; and the same is the case with electricity in the discharge of the Leyden phial; whence it is inferred, that in a thunder-storm it would be safer to have one's clothes wet than dry. Lightning burns, dissolves metals, rends some bodies, sometimes strikes persons blind, destroys animal life, deprives magnets of their virtue, or reverses their poles; and all these are well known properties of electricity.

2398. With regard to places of safety in times of thunder and lightning, Dr. Franklin's advice is to sit in the middle of a room, provided it be not under a metal lustre suspended by a chain, sitting on one chair, and laying the feet on another. It is still better, he says, to bring two or three mattresses or beds into the middle of the room, and folding them double, to place the chairs upon them; for as they are not so good conductors as the walls, the lightning will not be so likely to pass through them. But the safest place of all is in a hammock hung by silken cords, at an equal distance from all the sides of the room. Dr. Priestley observes, that the place of most perfect safety must be the cellar, and especially the middle of it; for when a person is lower than the surface of the earth, the lightning must strike it before it can possibly reach him. In the fields, the place of safety is within a few yards of a tree, but not quite near it. Beccaria cautions persons not always to trust too much to the neighbourhood of a higher or better conductor than their own body, since he has repeatedly found that the lightning by no means descends in one undivided track, but that bodies of various kinds conduct their share of it at the same time, in proportion to their quantity and conducting power.

SECT. II. Of the Means of Prognosticating the Weather.

2399. The study of atmospherical changes has, in all ages, been more or less attended to by men engaged in the culture of vegetables, or the pasturage of animals; and we, in this country, are surprised at the degree of perfection to which the ancients attained in this knowledge: but it ought to be recollected, that the study of the weather in the countries occupied by the ancients, as Egypt, Greece, Italy, and the continent of Europe, is a very different thing from its study in an island situated like ours. It is easy to foretell weather in countries where months pass away without rain or clouds, and where some weeks together, at stated periods, are as certainly seasons of rain or snow. It may be asserted with truth, that there is a greater variety of weather in London in one week, than in Rome, Moscow, or Petersburgh in three months. It is not, therefore, entirely a proof of our degeneracy, or the influence of our artificial mode of living, that we cannot predict the weather with such certainty as the ancients; but a circumstance rather to be accounted for from the peculiarities of our situation.

2400. A variable climate, such as ours, admits of being studied, both generally and locally; but it is a study which requires habits of observation and reflection like all other studies; and to be brought to any useful degree of perfection must be attended to, not as it commonly is, as a thing by chance, and which every body knows, or is fit for, but as a serious undertaking. The weather may be foretold from natural data, artificial data, and from precedent.

2401. The natural data for this study are, 1. The vegetable kingdom; many plants shutting or opening their flowers, contracting or expanding their parts, &c. on approaching changes in the humidity or temperature of the atmosphere: 2. The animal kingdom; most of those familiar to us exhibiting signs on approaching changes, of which those by cattle and sheep are more especially remarkable; and hence shepherds are generally, of all others, the most correct in their estimate of weather: 3. The mineral kingdom; stones, earths, metals, salts, and water of particular sorts, often showing indications of approaching changes: 4. Appearances of the atmosphere, the moon, the general character of seasons, &c. The characters of clouds, the prevalence of particular winds, and other signs are very commonly attended to.

2402. The influence of the moon on the weather has, in all ages, been believed by the generality of mankind: the same opinion was embraced by the ancient philosophers; and several eminent philosophers of later times have thought the opinion not unworthy of notice. Although the moon only acts (as far at least as we can ascertain) on the waters of the ocean by producing tides, it is nevertheless highly probable, according to the observations of Lambert, Toaldo, and Cotte, that in consequence of the lunar influence, great variations do take place in the atmosphere, and consequently in the weather. The following principles will show the grounds and reasons for their embracing the received notions on this interesting topic:

2403. There are ten situations in the moon's orbit when she must particularly exert her influence on the atmosphere; and when, consequently, changes of the weather most readily take place. These are,

1st, The new, and 2d, The full moon, when she exerts her influence in conjunction with, or in opposition to, the sun.

Sd and 4th, The quadratures, or those aspects of the moon when she is 90° distant from the sun; or when she is in the middle point of her orbit, between the points of conjunction and opposition, namely, in the first and third quarters.

5th, The perigee, and 6th, The apogee, or those points of the moon's orbit, in which she is at the least and greatest distance from the earth.

7th and 8th, The two passages of the moon over the equator, one of which Toaldo calls the moon's ascending, and the other the moon's descending, equinox; or the two lunistices, as De la Lande terms them. 9th, The boreal lunistice, when the moon approaches as near as she can in each lunation (or period between one new moon and another) to our zenith (that point in the horizon which is directly over our heads.

10th, The austral lunistice, when she is at the greatest distance from our zenith, for the action of the moon varies greatly according to her obliquity. With these ten points Toaldo compared a table of fortyeight years' observations; the result is, that the probabilities, that the weather will change at a certain period of the moon, are in the following proportions: New moon, 6 to 1. First quarter, 5 to 2 Full moon, 5 to 2 Last quarter, 5 to 4. Perigee, 7 to 1. Apogee, 4 to 1. Ascending equinox, 13 to 4. Northern lunistice, 11 to 4. Descending equinox, 11 to 4. Southern lunistice, 3 to 1.

2404 That the new moon will bring with it a change of weather is in the doctrine of chances as 6 to 1. Each situation of the moon alters that state of the atmosphere which has been occasioned by the preceding one: and it seldom happens that any change in the weather takes place without a change in the lunar situations. These situations are combined, on account of the inequality of their revolutions, and the greatest effect is produced by the union of the syzigies, or the conjunction and opposition of a planet with the sun, with the apsides, or points in the orbits of planets, in which they are at the greatest and least distance from the sun or earth. The proportions of their powers to produce variations are as follows:- New moon coinciding with the perigee, 33 to 1. Ditto, with the apogee, 7 to 1. Full moon coinciding with the perigee, 10 to 1. Ditto, with the apogee, 8 to 1. The combination of these situations generally occasions storms and tempests: and this perturbing power will always have the greater effect, the nearer these combined situations are to the moon's passage over the equator, particularly in the months of March and September. At the new and full moons, in the months of March and September, and even at the solstices, especially the winter solstice, the atmosphere assumes a certain character, by which it is distinguished for three and sometimes six months. The new moons which produce no change in the weather are those that happen at a distance from the apsides. As it is perfectly true that each situation of the moon alters that state of the atmosphere which has been produced by another, it is also observed, that many situations of the moon are favourable to good and others to bad weather.

2405. The situations of the moon favourable to bad weather are the perigee, new and full moon, passage of the equator, and the northern lunistice. Those belonging to the former are, the apogee, quadratures, and the southern lunistice. Changes of the weather seldom take place on the very days of the moon's situations, but either precede or follow them. It has been found by observation, that the changes affected by the lunar situations in the six winter months precede, and in the six summer months follow

them.

2406 The octants. Besides the lunar situations to which the above observations refer, attention must be paid also to the fourth day before new and full moon, which days are called the octants. At these times the weather is inclined to changes; and it may be easily seen, that these will follow at the next lunar situation. Virgil calls this fourth day a very sure prophet. If on that day the horns of the moon are clear and well defined, good weather may be expected; but if they are dull, and not clearly marked on the edges, it is a sign that bad weather will ensue. When the weather remains unchanged on the fourth, fifth, and sixth day of the moon, we may conjecture that it will continue so till full moon, even sometimes till the next new moon; and in that case the lunar situations have only a very weak effect. Many observers of nature have also remarked, that the approach of the lunar situations is somewhat critical for the sick. According to Dr. Herschel, the nearer the time of the moon's entrance at full, change, or quarters, is to midnight (that is within two hours before and after midnight), the more fair the weather is in summer, but the nearer to noon the less fair. Also, the moon's entrance, at full, change, or quarters, during six of the afternoon hours, viz. from four to ten, may be followed by fair weather; but this is mostly dependent on the wind. The same entrance during all the hours after midnight, except the first two, is unfavourable to fair weather; the like, nearly, may be observed in winter.

2407. The artificial data are the barometer, hygrometer, rain-gauge, and ther

mometer.

2408. By means of the barometer, Taylor observes, we are enabled to regain, in some degree at least, that foreknowledge of the weather, which the ancients unquestionably did possess; though we know not the data on which they founded their conclusions. Chaptal considers that the value of the barometer, as an indicator of the approaching weather, is greater than that of the lunar knowledge of the most experienced countryman, and indeed of all other means put together. (Agriculture appliquée à Chimie, &c.) We shall therefore annex such rules as have hitherto been found most useful in ascertaining the changes of the weather by means of the barometer.

2409. The rising of the mercury presages, in general, fair weather; and its falling foul weather, as rain, snow, high winds, and storms.

2410. The sudden falling of the mercury foretells thunder, in very hot weather, especially if the wind is south.

2411. The rising in winter indicates frost; and in frosty weather, if the mercury falls three or four divisions, there will follow a thaw; but if it rises in a continued frost, snow may be expected. 2412. When foul weather happens soon after the falling of the mercury it will not be of long duration; nor are we to expect a continuance of fair weather, when it soon succeeds the rising of the quicksilver.

2413. If, in foul weather, the mercury rises considerably, and continues rising for two or three days before the foul weather is over, a continuance of fair weather may be expected to follow.

2414. In fair weather, when the mercury falls much and low, and continues falling for two or three days before rain comes, much wet must be expected, and probably high winds.

2415. The unsettled motion of the mercury indicates changeable weather.

2416. Respecting the words engraved on the register plate of the barometer, it may be observed, that their exact correspondence with the state of the weather cannot be strictly relied upon, though they will in general agree with it as to the mercury rising and falling. The engraved words are to be regarded only as indicating probable consequences of the varying pressure of the atmosphere. The barometer, in fact, only shows the pressure of the aerial column; and the precipitation of rain, or the agitations of the atmosphere are

The

curial column, but are not necessarily connected with fluctuations of pressure. words deserve to be particularly noticed when the mercury removes from "changeable" upwards; as those on the lower part should be adverted to, when the mercury falls from "changeable" downwards. In other cases, they are of no use: for, as its rising in any part forebodes a tendency to fair, and its falling to foul, weather, it follows that, though it descend in the tube from settled to fair, it may nevertheless be attended with a little rain, and when it rises from the words " much rain" to "rain" it shows only an inclination to become fair, though the wet weather may still continue in a less considerable degree than it was when the mercury began to rise. But if the mercury, after having fallen to "much rain," should ascend to " changeable," it foretells fair weather, though of a shorter continuance than if the mercury had risen still higher; and so, on the contrary, if the mercury stood at “fair” and descends to "changeable," it announces foul weather, though not of so long continuance as if it had fallen lower.

2417. Concavity of the surface of the mercury. Persons who have occasion to travel much in the winter, and who are doubtful whether it will rain or not, may easily ascertain this point by the following observation: - A few hours before he departs, let the traveller notice the mercury in the upper part of the tube of the barometer; if rain is about to fall, it will be indented, or concave; if otherwise, convex or protuberant.

2418. Barometer in spring. Towards the end of March, or more generally in the beginning of April, the barometer sinks very low with bad weather; after which it seldom falls lower than 29 degrees 5 minutes till the latter end of September or October, when the quicksilver falls again low with stormy winds, for then the winter constitution of the air takes place. From October to April, the great falls of the barometer are from 29 degrees 5 minutes to 28 degrees 5 minutes, and sometimes lower; whereas, during the summer constitution of the air, the quicksilver seldom falls lower than 29 degrees 5 minutes. It therefore follows that a fall of one tenth of an inch, during the summer, is as sure an indication of rain, as a fall of between two and three tenths is in the winter.

2419. The hygrometer is of various sorts, but cord, fiddle-string, and most of the substances commonly used, become sensibly less and less accurate, so as at length not to undergo any visible alteration from the different states of the air, in regard to dryness or moisture. The most common of all barometers is that formed of the beard of the wild oat, Avèna fátua.

2420. A sponge makes a good hygrometer on this account, as being less liable to be changed by use than cord. To prepare the sponge, first wash it in water, and when dry wash it again in water wherein sal ammoniac or salt of tartar has been dissolved; and let it dry again. Now, if the air becomes moist, the sponge will grow heavier; and if dry, it will become lighter.

2421. Oil of vitriol is found to grow sensibly lighter or heavier in proportion to the less or greater quantity of moisture it imbibes from the air. The alteration is so great, that it has been known to change its weight from three drachms to nine. The other acid oils, or, as they are usually called, spirits, or oil of tartar per deliquium, may be substituted for the oil of vitriol.

2422. Steel-yard hygrometer. In order to make a hygrometer with those bodies which acquire or lose weight in the air, place such a substance in a scale on the end of a steel-yard, with a counterpoise which shall keep it in equilibrio in fair weather; the other end of the steel-yard, rising or falling, and pointing to a graduated index, will show the changes.

2423 Line and plummet. If a line be made of good well dried whipcord, and a plummet be fixed to the end of it, and the whole be hung against a wainscot, and a line be drawn under it, exactly where the plummet reaches, in very moderate weather it will be found to rise above such line, and to sink below it when the weather is likely to become fair.

2424. The hair hygrometer of Saussure, and the whalebone hygrometer, originally invented by De Luc, are esteemed two of the best now in use.

2425. The best and, indeed, only perfect hygrometer is that of professor Leslie. It consists of a siphon tube, with a ball blown at each end (fig. 208.), and filled with air. A coloured liquid fills one leg of the siphon; the ball on the opposite limb, smoothly coated with tissue paper, is the evaporating surface; this is kept perpetually moist by means of a thread passing from a jar with water as high as the instrument to the covered ball. The cold produced by evaporation causes the air in that ball to contract, and the coloured liquid is forced into that stem by the elasticity of the air included in the naked ball. This rise is exactly proportional to the dryness of the air. (T.)

208

2426. The rain-gauge, pluviometer, or hyetometer, is a machine for measuring the quantity of rain that falls.

2427. A hollow cylinder forms one of the best-constructed rain-gauges; it has within it a cork ball attached to a wooden stem (fig. 209.), which passes through a small opening at the top, on which is placed a large funnel. When this instrument is placed in the open air in a free place, the rain that falls within the circumference of the funnel will run down into the tube and cause the cork to float; and the quantity of water in the tube may be seen by the height to which the stem of the float is raised. The stem of the float is so graduated as to show by its divisions the number of perpendicular inches of water which fell on the surface of the earth since the last observation. After every observation the

209 cylinder must be emptied.

2428. A copper funnel forms another very simple rain-gauge: the area of the opening must be exactly ten square inches. Let this funnel be fixed in a bottle, and the quantity of rain caught is ascertained by multiplying the weight in ounces by 173, which gives the depth in inches and parts of an inch.

2429. In firing these gauges, care must be taken that the rain may have free access to them; hence the tops of buildings are usually the best places, though some conceive that the nearer the rain-gauge is placed to the ground the more rain it will collect.

2430. In order to compare the quantities of rain collected in pluviometers at different places, the instruments should be fixed at the same heights above the ground in all such places; because, at different heights, the quantities are always different, even at the same place.

2431. Thermometer. As the weight of the atmosphere is measured by the barometer, so the thermometer shows the variations in the temperature of the weather; for every change of the weather is attended with a change in the temperature of the air, which a thermometer placed in the open air will point out, sometimes before any alteration is perceived in the barometer.

2432. The scales of different thermometers are as follows:- In Fahrenheit's the freezing point is $2 degrees, and the boiling point 212 degrees. In Reaumur's the freezing point is 0, and the boiling point 80 degrees. In the centigrade thermometer, which is generally used in France, and is the same as that of Celsius, which is the thermometer of Sweden, the freezing point is 0, and the boiling point 100 degrees. As a rule for comparing or reducing these scales, it may be stated, that 1 degree of Reaumur's scale contains 2 degrees of Fahrenheit, and to convert the degrees of the one to the other, the rule is to multiply by 9, divide by 84, and add $2. ́ One degree of the centigrade scale is equal to one degree and eight tenths of Fahrenheit; and the rule here is to multiply by 9, divide by 5, and add 32. Any of these thermometers may be proved by immersing it in pounded ice for the freezing point, and in boiling water for the boiling point, and if the space between these points is equally divided, the thermometer is correct.

2433. The study of the weather from precedent, affords useful hints as to the character of approaching seasons. From observing the general character of seasons for a long period, certain general results may be deduced. On this principle, Kirwan, on comparing a number of observations taken in England from 1677 (Trans. Ir. Acad. v. 20.) to 1789, a period of 112 years, found:

That when there has been no storm before or after the vernal equinoz, the ensuing summer is generally dry, at least five times in six,

That when a storm happens from an easterly point, either on the 19th, 20th, or 21st of May, the succeed. ing summer is generally dry, at least four times in five.

That when a storm arises on the 25th, 26th, or 27th of March, and not before, in any point, the succeeding summer is generally dry, four times in five.

If there be a storm at S. W. or W. S. W. on the 19th, 20th, 21st, or 22d of March, the succeeding summer is generally wet, five times in six.

In this country winters and springs, if dry, are most commonly cold; if moist, warm: on the contrary, dry summers and autumns are usually hot, and moist summers cold; so that, if we know the moistness or dryness of a season, we can form a tolerably accurate judgment of its temperature. In this country also, it generally rains less in March than in November, in the proportion at a medium of 7 to 12. It generally rains less in April than October, in the proportion of 1 to 2 nearly at a medium. It generally rains less in May than September; the chances that it does so are at least 4 to 3; but, when it rains plentifully in May, as 18 inches or more, it generally rains but little in September; and when it rains one inch, or less, in May, it rains plentifully in September.

2434. The probabilities of particular seasons being followed by others have been calculated by Kirwan; and although his rules chiefly relate to the climate of Ireland, yet as there exists but little difference between that island and Great Britain, in the general appearance of the seasons, we shall mention some of his conclusions.

In forty-one years there were 6 wet springs, 22 dry, and 13 variable; 20 wet summers, 16 dry, and 5 variable; 11 wet autumns, 11 dry, and 19 variable.

2435. A season is accounted wet, when it contains two wet months. In general, the quantity of rain, which fall in dry seasons, is less than five inches, in wet seasons more; variable seasons are those, in which there fall between 30 lbs. and 36 lbs., a pound being equal to 157639 of an inch.

2436. January is the coldest month in every latitude; and July is the warmest month in all latitudes above 48 degrees: in lower latitudes, August is generally the warmest. The difference between the hottest and coldest months increases in proportion to the distance from the equator. Every habitable latitude enjoys a mean heat of 60 degrees for at least two months; which heat is necessary for the production of corn.

SECT. III. Of the Climate of Britain.

2437. The climate of the British isles, relatively to others in the same latitude, is temperate, humid, and variable. The moderation of its temperature and its humidity are owing to our being surrounded by water, which being less affected by the sun than the earth, imbibes less heat in summer, and, from its fluidity, is less easily cooled in winter. As the sea on our coast never freezes, its temperature must always be above 33° or 34°; and hence, when air from the polar regions at a much lower temperature passes over it, that air must be in some degree heated by the radiation from the water. On the