rain observations, and that expensive gauges of large diameters have no practical advantage over cheaper sorts.

397. A most important point requiring attention in the position of the rain-gauge is its height above the ground. Mr Phillips found the rainfall at York for twelve months during the year 1833-34 to be 14.96 inches at 213 feet from the ground; 19.85 inches at 44 feet; and 25.71 inches on the ground. An extensive series of observations has also been conducted by Colonel Ward, with the view of ascertaining the quantity of rain collected at different heights from the ground. The following is the relative rainfall at different times for the four years 1864-67 :-On a level with the ground, 1.07; at a height of 2 inches, 1.05; 6 inches, 1.01; 1 foot, 1.00; 2 feet, .99; 3 feet, .98; 5 feet, .96; 10 feet, .95; and 20 feet, .94. The Castleton observations give at 1 foot 1.00; at 5 feet, .96; and for 20 feet, .90. R. Chrimes's observations at Rotherham during 1866-67 give the following amounts: -At 1 foot, 1.00; 5 feet, .94; 10 feet, .91; 15 feet, .90; 20 feet, .89; and 25 feet, .88.

398. The remarkable fact here indicated, that different quantities of rain are collected at different heights, the quantity being greater at the lower levels, has been always confirmed whenever the experiment has been tried. No perfectly satisfactory account has yet been given of this singular phenomenon. The minute watery globules drawn gradually down from the rain-cloud in the train of the falling drops, and the downward course becoming horizontal as they near the surface, the greatest accumulation of such globules is near the surface, where, therefore, they coalesce in greatest numbers into drops. heavy enough to fall into, instead of floating past, the gauge; the eddies and currents which prevail most and strongest around isolated objects raised above the ground; the rebound of the finer particles into which many of the drops break as they strike with violence on the ground; and the condensing of the vapour of the atmosphere on the rain-drops as they fall through it, to a large extent account for the phenomenon. The first of these theories, which has been proposed by

James Dalmahoy, Edinburgh, would appear to account for the greater part of the excess of rain collected in gauges nearest the surface. The last of the theories, being that proposed by Dr Franklin, and long accepted as sufficient, can only, according to Sir John Herschel, account for one-seventeenth part of the observed excess. The eddy theory advocated by Mr Jevons is interesting, as affording an explanation of many of the anomalous results which have been obtained; while the remaining theory serves to explain the greater part of the excess observed from one foot downwards to the surface. Since no gauge can ever be constructed and placed so as to measure with perfect accuracy the quantity of rain which falls on the ground, it is only necessary to secure, as far as possible, that all gauges be similarly constructed and placed in positions similar to each other.

399. Rain is the most capricious of all the meteorological phenomena, both as regards its frequency and the amount which falls in a given time. It rarely or never falls in certain places, which are on that account denominated the rainless regions of the globe: the coast of Peru, in South America; the great valley of the rivers Columbia and Colorado, in North America; the Sahara, in Africa, and the desert of Gobi, in Asia, are examples: whilst, on the other hand, in such places as Chiloe and Patagonia, it rains almost every day.

400. The quantities of rain which have been recorded as having fallen at one time in some places are truly enormous. In Great Britain, if an inch falls in a day, it is considered a very heavy rain. But in many parts of the Highlands of Scotland, 3 inches not unfrequently fall in one day. On the 5th December 1863, there fell at Portree, in Skye, 12 inches in 13 hours, during which a continuous cataract appeared to fall from the roofs of the houses; and on the same day 5.2 inches fell at Drishaig, near Ben Cruachan, in Argyleshire, where also two days afterwards 7.12 inches fell in 30 hours. At Seathwaite, in Cumberland, 6.62 inches fell on 27th November 1848; and this enormous fall in one day has been nearly reached six times since that date. But it is in lower

latitudes that the heaviest single showers have been recorded. The following are a few of the most remarkable :At Joyeuse, in France, 31.17 inches in 22 hours; at Genoa, 30 inches in 24 hours; at Gibraltar, 33 inches in 26 hours; on the hills above Bombay, 24 inches in one night; and on the Khasia Hills, north-west of Calcutta, 30 inches on each of five successive days.

401. Rainy Days.-Rainy days are more numerous in high than in low latitudes. Thus, in the northern hemisphere, from 12° to 43° latitude, the number of rainy days in the year is, on an average, 78; from 43° to 46° latitude, 103; from 46° to 50° latitude, 134; and from 50° to 60° latitude, 161. Considerable discrepancy exists among observations as to the number of rainy days, owing to the want of a generally received definition of what constitutes a rainy day. The fall of .01 or inch of rain, as suggested by Mr Symons, is now

very generally adopted.

402. Rainfall within the Tropics.-At places within the tropics where the trade-winds are blowing regularly and steadily, the rainfall is small, because, these winds coming from higher latitudes, the temperature is increasing, and they are thus rather in the condition of taking up moisture than of parting with it; and the return trades, which blow above them in the opposite direction, having discharged the greater part of their moisture in the region of calms, are also dry and cloudless. Where, however, the trade-winds are forced up the slopes of mountain-ranges lying in their course, as on the east of Hindostan, they bring rain in copious showers.

403. The Region of Calms is a broad intertropical belt about 5° in breadth, where the north-east and south-east trades meeting, mutually destroy each other, and thus produce a calm. This is the region of constant rains. Here the sun almost invariably rises in a clear sky; but about midday clouds gather, and in a short time the whole face of the sky is densely covered with black clouds, which pour down prodigious quantities of rain. Towards evening the clouds disappear, the sun sets in a clear sky, and the nights are serene

and fine. The reason of this daily succession of phenomena in the belt of calms is, that there the air, being greatly heated by the vertical rays of the sun, ascends, drawing with it the whole mass of vapour the trade-winds have brought with them, and which has been largely added to by the rapid evaporation from the belt of calms; this vapour is condensed as it rises to the line of junction of the lower and upper trades. The discharge is in some cases so copious that fresh water has been collected from the surface of the sea. As evening sets in, the surface of the earth and the superincumbent air being cooled, the ascending currents cease and the cooled air descends; the clouds are thus dissolved, and the sky continues clear till the returning heat of the following day brings round a recurrence of the same phenomena. It will be observed that the daily rains of the belt of calms are to some extent analogous in their origin and causes to the formation of the cumulus cloud of temperate climates. Since the belt of calms which determines the rainy season within the tropics moves northward or southward with the sun's declination, carrying the trade-winds with it on each side, it follows that there will be only one rainy and one dry season in the year at its extreme northern and southern limits, but at all intermediate places there will be two rainy and two dry seasons, these being at the equator equally distant from each other.

404. This state of things is only strictly applicable to the Pacific Ocean, whose expanse of water, presenting a uniformly radiating and absorbing surface, is sufficiently broad to allow the law to take full effect. But over a great part of the tropics disturbing influences draw the trade-winds out of their normal course, and sometimes, as in the case of the monsoons, give rise to winds which blow from the opposite point of the compass. These winds determine the rainfall of India, and but for them the eastern districts of Hindostan would be constantly deluged with rain, and the western districts constantly dry and arid. As it is, each part of India has its dry and wet seasons, summer being the wet season of the west and interior as far as the Himalaya, and winter the

wet season of the east, and especially the south-east. Thus the rainfall at Mahabuleshwar, in the Western Ghauts, in the four months from June to September, is 242 inches, while during the other eight months it is only 12 inches. At Benares for the same time the quantities are 46 inches and 7 inches. On the other hand, in the east, at Madras, the rainfall for the three months, October, November, and December, is 30 inches, and for the other nine months 19 inches.

405. So far as known, the heaviest annual rainfall at any place on the globe is 600 inches, on the Khasia Hills, about 500 inches of which fall in seven months, during the southwest monsoons. This astonishing quantity is due to the abruptness of these hills facing the Bay of Bengal, from which they are separated by only 200 miles of low swamps and marshes. Hence the southerly winds not only arrive heavily laden with the vapour they have licked up from the Indian Ocean, but, receiving further accessions of moisture in passing over the 200 miles of swamp, they are, so to speak, ready to burst in torrents, even before they are suddenly raised, by the hills they encounter, into the cooler regions of the atmosphere. At 20 miles farther inland the annual amount is reduced to 200 inches; at 30 miles to 100 inches; north, at Gowahatty, in Assam, it is only 80 inches. In the northwest of the Bay of Bengal, at Cuttack, it is only 50 inches; while in the north-east, in Arracan, being more in the course of the south-west monsoon, the rainfall is swelled to 200 inches. In the following annual amounts the effect of the hills is strikingly shown:-At Madras, 55 inches, but Seringapatam only 24 inches; at Bombay, 75 inches; among the West Ghauts, at Uttra-Mullay, 263 inches; and at Mahabuleshwar, 254 inches; while at Poonah, more inland, it is only 24 inches. In Mauritius, for the four years ending 1865, the average rainfall at Gros Cailloux was 29.84 inches, whereas at Cluny, only about 16 miles distant, it amounted to 146.17 inches. In regard to the above, Mr Meldrum remarks: "At Cluny, in the vicinity of mountains and forests, in the southeast part of the island, and exposed to the trade-wind as it

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