Some valuable observations on waterspouts formed over land have been recently made by 3lajor Walter S. Sherwill, an officer to whom we are indebted for various contributions to science, respecting the physical geography and meteorology of India. Among other instances, he has described in a very instructive manner a waterspout of colossal dimensions which was seen to form and burst at Dun Dum, eight miles north-east of Calcutta, on the 7th of October, 1859. The circumstances preceding and attending the phenomenon were as fol lows : The south-west monsoon [MoNsooN] during the week had received its first check by the north-east monsoon endeavouring to cross the Himalaya mountains, and to drive back the heavy masses of clouds " and moisture " (probably clouds becoming floating small rain, having the aspect of mist) that had been banked up along their flanks during the whole of the rainy season, or during the prevalence of the south west monsoon. At Dum sum, the visible heavens were wholly occupied by a dense mass of very grandly shaped and massively grouped strata of cumuli [Ctoun] at various elevations; the lowest stratum, from actual measurement by Major Sherwin, was 2000 feet above the earth, the highest probably reaching the altitude of 25,000 feet, the entire mass being about five miles in vertical thickness. The aspect of the heavens during the past few days had been most remarkable, presenting a scene of great disturbance ; the clouds, evidently impelled from the south by the south-west monsoon, but., checked by the north-east, the whole mass, extending for as many miles as the eye could reach from north to south and from east to west, acquired a rotary and at the same time an undulatory motion ; huge tracts of clouds revolving rapidly around a centre which appeared, from the observer's position, distant about 1/ mile from Dum Dum, to be about 5 miles to the south-east. This rotary motion, performed in a very large circle, gave the clouds the appearance of moving in two distinct directions, those nearest to the observer appearing to be going north, and those furthest removed to be going south. In the early portion of the day, the wind had been from the south, bringing with it. from the sea a large body of clouds; at noon it changed to the south-west, at 2 PAL to the west, and at 4 P.M. to the north : there had been but little rain during the day.
The greatest disturbance in the clouds took place between the hours of three and four, the whole mass revolving and heaving violently ; extensive masses of clouds were crushed and driven into others, but no lightning was observed. It now rained heavily to the north and east. " During this time," Major Sherwin says, " more than one waterspout endeavoured to form, but unsuccessfully. It was whilst observing the highly-agitated masses of clouds that were revolving and oscillating in a most peculiar manner, that I witnessed the commencement and ter mination of the remarkable waterspout now under consideration. At three P.M. it became suddenly quite calm, and during the calm a pale but very watery, cumulus, the base of which was a right lino, and el to the horizon, was seen to bulge out downwards or towards earth in a long well-defined and light blue coloured out line; from the centre of this hanging curve a broad column of a pale watery vapour rapidly sank towards the earth, closely resembling a very attenuated cone, dark at the edges and pale blue in the centre, plainly showing it to be a solid cylinder; as it neared the earth the lower half of this elegant column commenced to gyrate rapidly, the lower end oscillating violently to the right and to the left ; this latter movement I imagine to be a more optical illusion, caused by the lower end of the column revolving in a circle of large diameter; as the column neared the earth it expanded and contracted in an agitated and rapid manner about the centre into cloudlike protuberances, which partook at the same time of the motion of the revolving column.
Upon arriving nearer the earth tho and of the column parted into two slender columns about 150 (' or 200,' as stated in another place) feet each in length, and In this condition reached the ground. The shape of the column was now completely and instantaneously altered ; for the whole cumulus burst, and was seen pouring down to the earth, not ria a shower of rah, but as a limn? mass of water, resembling a waterfall i more than a shower of rain, that completely exhausted and brought the whole cloud to the ground in a few seconds of time." The estimated length of the cumulus, the lower portion of which had become a heavy nimbus, from which the waterspout depended, had been 3000 feet, and its height, from base to summit, 5000 feet. By trigonometrical means, Major Sherwin ascertained that the perpen dicular height or length of the column or waterspout itself, from the point of its protrusion from the clouds to its lowest extreme point, at. the moment of bursting, was 1500 feet. Its period of duration, from its first formation to its bursting, was about 25 seconds. It burst upon the artillery practice-ground, a large grassy plain, of which it covered half a square mile with water to the depth of about half a foot, which took fourteen days to drain off by tho usual drainage courses of the country. The cattle fled in all directions as it descended, but no noise was heard at tho observer's position.
Major Sherwill's observations are illustrated by excellent lithographic representations of the waterspouts he observed. Some of these aro somewhat roughly copied in the subjoined diagram, in which fig. 3 represents the waterspout now described. Half an hour after this had disappeared, be relates," another formed to the east of the position : it was a very attenuated column, about 900 or 1000 feet in length, but the cloud from which it descended being upwards of 2000 feet above the earth, no contact was completed ; the column, which lasted for half-an-hour, gradually faded away, being absorbed upwards into the cloud from whence it. had descended. The cloud and column were moving rather rapidly towards the south, which probably accounts for the column never reaching the ground. The column gyrated and oscillated violently, lengthening and contracting as shown iu the diagram (fig. 4), where eleven different positions of the column are given, sketched at intervals of from two to five minutes. Towards sunset, the clouds began to yield to the north wind, and were gradu ally driven out to sea, leaving a clear cloudless sky ; and at nine o'clock at night not a cloud was to be seen. The north-east monsoon had fairly set in.