WEATHER, CLIMATE, AND TEMPERATURE—ISOTHERMAL LINES—ISOBARS, WEATHER FORECASTS, AND SIGNS OF THE SKY.

It is usually considered a sign of a paucity of ideas when one begins a conversation about the “weather,” but there can be no doubt that there is no more interesting question in social life at certain times as to whether it will or will not rain. Our outdoor amusements are all dependent upon weather, and a little cloud may throw a deep shadow over all our pleasure if we neglect to bring out an umbrella, or to carry a waterproof. We are never independent of what we term the “capricious” climate, but in reality the laws of “the Weather,” though so imperfectly understood, are fixed and invariable, and if we could read the signs in the sky and learn the condition of the atmosphere, we might leave the “prayers for rain” and “for fine weather” out of the Church service, for then we should understand that unless miracles are performed for us the laws of Nature can in no wise be altered.

Of late years weather forecasts (not prophecies) have come before us in our newspapers after the manner instituted by the late Admiral Fitzroy, whose name has become a household word in England. But at the commencement of the Christian era and before that time the signs of the heavens and the behaviour of animals and birds were noted with reference to changes of weather. If we read Virgil we shall find numerous references to these portents, and the translation usually quoted will furnish us with information which must be as true nowadays as it was in Virgil’s time, for wild animals do not change their habits. Speaking of wet weather in the Georgics the poet wrote:—

We might quote further selections respecting the signs in the heaven and earth mentioned, but the foregoing verses will be sufficient to illustrate our position, and to show us that weather forecasting is, at any rate, as old as the Christian era.

The moon is generally supposed to influence the weather—a “Saturday’s Moon” being particularly objectionable, or when she appears anew at some hours after midnight thus—

Weather permitting, we can go out and study the clouds as described in the foregoing chapters, or consult the barometer, and see which way the wind blows. The child will tell us that a high “glass” means fine weather, and a low barometer indicates rain, but this is only relatively true. A high glass may be falling, a low glass may be rising. A sudden fall or a sudden rise are indicative of bad, windy weather, or a short-lived fine period. The glass may rise with a northerly wind, and rain will supervene, so careful observation is necessary before one can obtain even a superficial knowledge of the weather. (See subsequent observations on “Weather.”)

The Americans telegraph the results of their observations of coming storms across the Continent, corrected by the signs noticed and recorded by vessels arriving in New York. Thus they are frequently very accurate; steady application and observation at Sandy Hook must give them a great deal of useful information for the “forecasts.”

The word Climate is derived from the Greek klima, a slope; and thus at a glance we perceive how the aspect it presents to the rays of the sun in the earth’s revolutions, must affect the “climate” of a country. Of course the position of any portion, the elevation and locality of the mountains, have also a share with the soil, winds, rains, and sea-board, in determining the climate of any region. Many points have already been touched upon in former chapters. Temperature, moisture, and vegetation are the chief natural features which determine climate, and we must find out the position of the land with reference to the sun first, to ascertain the climate.

The more vertical the sun is the hotter the atmosphere, for the rays strike directly upon the earth, which radiates the warmth received. These heat rays are, as we know, invisible. The hottest portion of the earth must be at the equator for the sun is overhead, and the rays beat down directly upon the earth. The sun is also nearer than when at the horizon, and less rays are absorbed by the atmosphere. The longer the day the greater the heat.

Temperature is registered by observation of the thermometer, and the distribution of heat is represented upon a chart across which lines are drawn at places of equal temperature. These lines are called “isothermal.” There are also terms to denote equal winter temperature and the average summer heat—isochimines and isotheres respectively.

Temperature decreases as we ascend from, and increases as we descend into, the earth. This fact proves that the air is not warmed by the sun’s heat, but by radiation from the ground. As we ascend we reach the line of perpetual snow, which varies in different parts of the globe. In the tropics it extends from 15,000 to 18,000 feet; but it varies even in places of the same latitude, according as the towns are inland or on the coast, as in the Pyrenees and Caucasus, where there is a difference of three thousand feet in the snow limit.

The line of the snow limit, as a rule, gets lower as we journey from the equator to the poles. Exception will be found in the HimÂlaya, where the snow line is higher on the northern side, in consequence of the existence of the Thibetan tableland, which causes a higher temperature than that existing upon the abrupt southern slope. Countries, therefore, though in the same latitude, may have different climates according to the elevation of the land.

The proximity to the sea is another reason for climatic difference. Water takes some time to become warm, but when it has once become so it will not readily part with its heat. The Gulf Stream, with its warm current beating along our shores, gives us a high temperature and a moist climate—a very different condition to Newfoundland or Nova Scotia, which are in much the same latitude as England and Ireland. By the sea the climate is more uniform, and the extremes of heat and cold are not so distant. We send invalids to the seaside to save them the effects of such violent changes. Winters are milder and summers cooler by the sea.

We can readily understand how such circumstances affect the vegetation, and places which in winter may enjoy a mild and genial climate (comparatively speaking), may have a cold summer. Ferns may flourish in winter out of doors, but wheat will not ripen in the autumn owing to the want of heat.

The winds also, and the soil and aspect of a region, all have a share in determining its climate. Trees bring rain by evaporation, and a wooded country is a blessing to its inhabitants, defending their habitations from wind and avalanches in mountainous districts. But the climatic conditions are altering. The ground is being more and more cleared; the soil is more cultivated, and moisture is being more eliminated from it. Therefore the air becomes warmer by the radiation of the ground, and clouds are formed which keep the warm layers down nearer the earth. Mountains, as we have seen, affect the rain-fall in districts; and in Scandinavia—in Norway chiefly—the average rain-fall is very high. The sheltering effects of mountains from east or northerly winds also alter the climate, while clay or gravel soils are cold or warm inasmuch as they absorb, or evaporate, moisture. Some surfaces being different from others give out more heat.

In some mountainous districts we shall find every variety of climate from the sea-level tropical heat to the rigours of the pole. The greatest average temperature is north of the equator in Africa; the lowest in the north, to the west of Greenland. Masses of land act in a different manner to the oceans, and the former become heated and cooled with equal rapidity, while the sea, as already mentioned, is slow to lose its heat. Our land enjoys a mild and equable climate as a rule, because it is surrounded by water, and the Gulf Stream warms it. The European climate, taken altogether, may be considered the best on the globe.

We will now pass on to a few observations concerning the weather, and the means of determining it beforehand.

It is always a dangerous thing to act the part of a prophet, and the uncertainty attending an uninspired foreteller’s predictions must in time disparage him in the estimation of his hearers and disciples. But there are signs in the sky which we can discern and render valuable by the aid of instruments. We must have a reliable barometer and thermometer, and keep a record of the average conditions of the weather, if we wish to wear the mantle of the weather-prophet—a term now, in America, applied (jokingly, no doubt) to people who are not particular in their statements of facts.

But without entering upon any scientific discussion, we may state a few plain rules which can be observed, besides the indications of a rising or falling barometer. Having frequently studied the aspects of the clouds, with the assistance of the hints from the wind-currents, we can fairly prognosticate or suggest probable changes of weather.

We have already remarked upon the colours of the sunset, which are attributable to the vapours in the atmosphere, and we say a red sky foretells fine weather; a yellow sky changing into green means rain, or rain and wind; on the other hand, when the red rays appear we may anticipate fine weather, as the atmosphere is becoming less and less moist.

A “low” dawn is known as a good sign; so when the first rays appear at, or near the horizon, we may anticipate a fine day, as we may when the morning is grey.

“Evening red and morning grey”

are almost unfailing tokens of fine weather.

Very often a yellow sunset means wind; a wild, crimson sky means a gale. On the afternoon (Saturday) before the Eurydice foundered off the Isle of Wight, we particularly noted the sunset at Gravesend; and it was evident (in our estimation) that a sudden storm was imminent, and we remarked it to our companions. The sudden fall of the barometer, and the appearance of the rising clouds early on that sad Sunday afternoon, approaching in dark masses from the west and north-west, spoke of rain and (possibly) snow. How true the forecast was the event proved.

When clouds are soft and thin we expect fine weather; when they are dark and hard, rain and wind. A ragged-edged and heavy cloud indicates thunder and lightning, with squalls when we see dark clouds flying rapidly across the mass of cumuli. A “mackerel” sky and “mares’ tails” generally foretell wind, the direction and the upper currents being noted. The longer the warning given by the heavens, the longer the bad (or fine) weather will last; and the converse is also true.

The cirrus is a wispy cloud, and is often observed extending across the sky on a fine afternoon. This may or may not indicate rain; it generally points to wind. If its direction be northerly and west to southerly and east, it is a good sign, but from west to east it is a bad sign. The habits of birds and animals, and their anxiety for shelter, “pigs running with pieces of straw in their mouths,” and the low-flying swallow, are all signs of approaching rain and bad weather, and the scintillation of stars betokens moisture in the atmosphere. These are well-known appearances, but there are others regarding the winds and currents of air which require the assistance of Admiral Fitzroy’s book.

For instance, a falling barometer with rising temperature means southerly winds and rain; in winter, with low temperature, snow.

But a rising barometer with northerly wind often means rain.

A rising glass after a low fall may, and often does, indicate more wind from the north, and after that fine weather, if lower temperature also supervene. If warm weather continue under the circumstances, the wind may back and blow from the southward.

“The most dangerous shifts of wind happen soon after the barometer rises from a very low point, or if the wind veers gradually shortly after with a rising barometer.”

If the barometer rises with a southerly wind fine weather may be expected, and if it falls with a northerly wind rain, hail, and snow are imminent, for the rule is a fall for southerly, and a rise for northerly winds.

A sudden fall with west wind indicates storm from northerly quarters (N.E. to N.W.). An east gale veering southwards with falling glass indicates a change of storm-direction to a point from N.W. or N.E., suddenly and violently, though a change might have been expected from the appearance of the glass. A calm frequently occurs between these disturbances.

A backing wind—that is, a wind going in a direction opposed to the sun’s course (and with the earth)—is a bad sign after unsettled weather. The wind is said to “veer” when it goes with the sun.

The south-east wind, with clear sky, warm weather, and low clouds on the horizon, is a sign of wet. A dry east wind means fine weather. Heavy clouds in the north-west generally bring a thunderstorm. When really distant objects look very near rain must be expected.

There are many exceptions to weather rules, and none can be laid down as invariable. The ever-changing currents of air, and varying moisture of the atmosphere, give rise to barometric changes, which should be carefully noted. A little experience and close observation for one year, with notes of signs, and indications of temperature, will assist any one to tell the probable change that is approaching.

There are a great number of signs of weather which are observable in the animal and even in the vegetable kingdom, as well as in the moon and stars. Many flowers close their petals before rain comes on, and the behaviour of domestic animals often foretells storm. Sheep huddling together in a corner tell us the direction from which the tempest is approaching; sea birds fly to shore, and land birds become restless.

The naturalist will observe the domestic animals which become uncomfortable and sniff the air; the cat lies with her head down, the brain lowest; and frequently washes her face, or scampers about aimlessly. Spiders disappear, and worms come up to seek the expected water. When fine weather is coming all nature appears glad, but leeches sink into the water as far as they can.

The above are some of the domestic and common signs of coming rain, and conversely for fine weather. A wailing wind, a cloudy mountain, a greenish rainbow or too red a one, a pale moon with indistinct points, or a halo round it, are all signs of rain and possibly wind. So the most superficial observer may with these few suggestions inform himself of the chances of fine or wet weather.