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RAINFALLS:

LAWS GOVERNING THEM.

In general, the nearer the sea, the more elevated the situation, and, if not on a hill, the nearer its vicinity and the more prevalent the direction of the wind is from the sea—especially if while coming from the sea it blows from a southerly direction in the northern hemisphere, and from a northerly direction in the southern hemisphere—the greater is the annual amount of rain for the latitude. On the contrary, the farther distant from the sea, and the flatter and more low-lying the country—particularly if mountains intervene between the place of observation and the sea, and if these be distant from the place of observation at least twenty miles—the less rain ought to fall for the latitude.

The localities where the greatest amount of rain falls for the latitude are probably on mountains near the sea, of the height of 2000 feet and upward in warm climates, and 1500 feet and upward in temperate latitudes. Such mountains, owing to their annual rainfall, give birth to almost all, if not all, the large rivers of the world. Thus the summits of the Port Royal Mountains in the Island of Jamaica are enveloped in clouds, and rain there falls in torrents every forenoon even during the dry season, when in intertropical climates generally, except over or in the vicinity of mountains, clouds or rain seldom make their appearance.

Provided mountains be 6000 feet or more in height in temperate and cold climates, and 7000 feet or more in warm climates, the rain is almost wholly precipitated on their windward sides, and hardly any falls to leeward of them. The reason of this is, that all the denser species of clouds, which produce rain in champaign, low-lying countries, usually float at a lower altitude than 6000 or 7000 feet. This explains the reason why little or no rain falls in a large portion of Peru lying to the west and leeward of the Andes, whereas it rains almost incessantly on the eastern flanks of that elevated range of mountains.

If mountains varying in height from 1200 to 3000 feet lie immediately to the leeward of any place, or even suppose a place be entirely surrounded by such, instead of affording protection from rain they greatly increase its amount. Thus, at Keswick, in the north of England, which lies in a hollow, surrounded almost in every direction by, and not farther distant than a mile or two from, hills varying in height from 1000 to 3000 feet, more rain falls than in any other place that has yet been examined in England. The mean annual amount of rain which falls there is no less

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than 67.5 inches; while at Upminster, in the flat county of Essex, unprotected by any hills, the mean annual amount is only 19.5 inches. To understand the explanation of the former of these cases, it must be recollected that the aqueous vesicles which form clouds do not descend to the earth's surface until their specific gravity is increased by the slow and gradual process of aggregation into what are called drops of rain. Though mountains, therefore, of moderate elevation may cause a precipitation of moisture from the atmospheric current while passing over them, still a large proportion of that moisture is wafted by winds to a greater or less distance in the form of clonds. Now, the excess of rain in the vicinity of mountains is partly, is not principally, owing to the influence of their elevated rugged summits and irregular intersecting valleys in producing a generally agitated state of the atmosphere and a conflict of aërial currents moving in somewhat different directions; and the mechanical effect of such circumstances is to drive together and congregate the component vesicles of clouds into drops of rain, and thereby accelerate their descent to the earth.

At a distance, however, of twenty miles or more to the leeward of hills of the above-mentioned moderate elevation the amount of water preci. pitated among the hills and returned to the sea by rivers essentially contributes to the hygrometric dryness of the atmosphere and to a diminution of the amount of rain. Before reaching this distance from the mountains the atmospheric current has again recovered its uniform unagitated progressive movement, and, unless the formation of clouds arising from some other cause be going on, the remainder of the clouds formed by the mountains, not previously precipitated to the earth's surface in rain, is by this time either dissolved, or so far in progress of dissolution by evaporation as to be incapable of producing rain.

The annual amount of rain that falls near the western coast of Britain is in general greater than what falls near the eastern coast. This is owing to the circumstance of air becoming usually hygrometrically drier the farther it passes over land, in connection with the fact of winds from the south-west being more prevalent in this island than winds from the south

Nor is a wind blowing from the sea toward the land necessarily a rainy wind, provided the land be warmer than the sea from which it blows. In such circumstances, as the atmosphere progresses over the land it gradually becomes warm and more under-saturated, and accordingly less apt to give birth to clouds and rain. This is the reason it almost never rains in Egypt, though the wind during a large proportion of the year blows from the Mediterranean. The aqueous vapor raised from that inland sea is carried with a northerly wind unprecipitated till

east.

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it comes into collision with the elevated mountains in the kingdom of Abyssinia.

As the aggregate amount of heat which the earth annually receives from the sun, and the amount of moisture annually evaporated from the earth's surface, probably undergo little or no variation, the aggregate amount of rain which falls on the earth's surface must in like manner be similar every year. Hence, in conformity with this principle, it may be inferred that wetter seasons than ordinary in one country or climate are simultaneously balanced by seasons proportionally drier than ordinary in some other country or climate. Such differences are wholly to be ascribed to variations in the direction and force of the winds in different seasons; and it is further probable that the differences in the prevailing direction and force of the winds are also regulated according to some compensating principles, by which different countries within a limited number of years are supplied with their relative mean proportions of rain.

RED AND YELLOW RAIN.

It is recorded, upon authentic evidence, that rain sometimes of a yellow and sometimes of a red color has on rare occasions been observed to fall in various places. In these cases the coloring-matter appears to have been derived from vegetable pollen of the colors described, transported by winds and precipitated to the earth along with showers of rain.

Snow of a red color has also been observed in Iceland and other places in the northern regions. The coloring-matter in one case was supposed to be a mixture of red ashes ejected during a volcanic eruption in the neighborhood. That vegetable pollen, one of the lightest and most transportable of all substances, should be carried by wind and precipitated to the earth by a shower of rain, is by no means unlikely; and to such an occurrence doubtless we may attribute the reports of “red rainfalls."

The heaviest fall of rain on our globe takes place on the Khasia Hills, to the north-west of Calcutta, and amounts to 600 inches annually. The greatest amount that has fallen in the vicinity of Montreal in one hour was 1.110 inches.

Below is a table showing the annual mean amounts of rainfall at some of the principal stations on our globe. The amount is in inches and tenths:

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Inches. 52.31 48.63 44.48 43.44 42.10 41.20

40.98

Vera Cruz.........
Bergen
Rio Janeiro........
Sierra Leone.....
Canton...........
Bombay ....
Barbados.
Mądras .....
Cork
Rome.
Brussels....
Naples.
Oxford.....
Paris.
London
Stockholm..
Copenhagen....
St. Petersburg....

Inches.
.183.00 New Orleans..........

89.00 Cincinnati....
89.00 Cambridge.........
87.00 Halifax.
78.00 St. John, N. B............
75.00 Washington.......
72.00 Baltimore....
55.10 Albany..
40.00 Quebec..........
30.86 Manchester...
29.96 Montreal...
29.94 Liverpool..........
27.10 Toronto....
22.64 Aberdeen.....
22.00 New York.........
19.67 Dublin...
18.55 San Francisco.............
17.65 Glasgow......

40.67 39.10 36.00 36.00 34.00 31.50 28.87 28.63

24.00 ..... 22.00

21.33

WHEN the whole sky is covered with clouds, their further formation and increase in bulk and density is indicated by their descent to a lower level, and their decrease by their ascent. Accordingly, when clouds begin to sit down upon the tops of hills, it prognosticates rain; and when they begin to rise above the hills, it prognosticates dry weather.

Mist extending upward from the surface of the earth on a summer morning foretells a dry, warm day. The country-people call such a mist heat, meaning thereby that it bespeaks a hot day. Such mists result from coldness, induced upon the earth's surface by the radiation of caloric during night, being propagated upward to the atmosphere in sufficient intensity to produce atmospheric over-saturation, and the precipitation of moisture in the forms of dew and mist. This only happens during calm, starry, cloudless nights, which are the usual concomitants, and among the most certain prognosticators, of dry, settled weather.

THE St. Lawrence River was lower during April, 1881, than at any previous time in a long period of years, while in the West and South westward most damaging floods were experienced.

HOW MAN AND THE ANIMALS ARE AFFECTED BY THE

WEATHER-CHANGES.

PERSONS subject to rheumatism frequently write to me relative to their barometric propensities, and did the limited space permit I could furnish many a laughable letter respecting the numerous indications of the weather given by the “twinges” of afflicted individuals. The fact is, that persons subject to rheumatism and like complaints become affected, probably upon hygrometric principles, when the atmosphere becomes damp, and feel relieved when dry weather returns. Such individuals may be considered living hygrometers.

What is a hygrometer? I know many of the readers of the Almanac will at once inquire. This instrument was briefly described in my Almanac for 1877–78 (page 97). The principle upon which it has been generally constructed is that a certain degree of affinity exists between moisture and air and moisture and many other substances that one substance attracts another for which it has an affinity with proportionately less force according as it is more nearly saturated with it. Thus, a hair or piece of catgut may be used for hygrometric purposes, for either of these substances exerts a certain degree of attraction for moisture. Accordingly, as the air gets more nearly saturated, and exerts a proportionately less attractive force for humidity, these substances absorb a greater amount of moisture, and in so doing expand in thickness but diminish in length. On the other hand, when the air becomes drier than usual, and exerts a proportionately stronger attraction for moisture, a portion of humidity is abstracted from these bodies; and this, while it diminishes their thickness, increases their length. Hence the length of such or similar substances, fitted up and adjusted to a scale of equal parts according to various mechanical contrivances, has been employed as a measure of the dryness and dampness of the atmosphere.

Another principle upon which hygrometers have been constructed is based upon the different degrees of rapidity with which moisture evaporates and reduces the temperature of the evaporating surface, according to the state of the atmosphere as to humidity. As, however, I do not mean to describe meteorological instruments generally, this point need not be further enlarged upon. One object in remarking upon such instruments is, that if the principles of their construction be correctly understood a great mass of weather-indications held in esteem by the more

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