and South America, and suggest the mode of formation of the great deserts. Ascending to the earlier periods of geology, it will account for the situs of the aqueous deposits in those periods, as the post-pliocene, tertiary, and cretaceous. The views presented in the memoir are the result of a study of the tidal currents on the alluvial shores of the United States, and particularly on the New England coast. This study has led to the discovery of a threefold relation in form, amount, and locality between these currents, and the materials transported by them. The certain relation between the tidal currents and the alluvial deposits in structure, position, and amount establishes a principle of conformation in the latter, by means of which the geologist will be enabled to reason back from the deposits of earlier periods to the nature of the currents by which they were made, as the character of the present formations on the borders of the sea and in its depths is readily decided when the peculiarities of the local currents are ascertained." [This memoir has been printed in extenso in the current volume of the Memoirs of the Academy, Vol. IV., New Series.]

Dr. Pierson read a communication from Dr. Usher Parsons, of Providence, giving a detailed account of a tornado that passed near Providence, Rhode Island, at 3 o'clock, P. M., taken from minutes made at the time.

"Whilst a heavy rain was falling, a black cloud was seen in the west, which seemed to send down towards the earth a very dark elongated cone. It commenced its career, as its traces afterwards proved, in Johnston, about five miles west-southwest of Providence, and moved in a north-northeast direction, at the rate of ten or twelve miles the hour, passed across the head of Narraganset Bay, and moved onward in a straight line eight or ten miles, towards Dighton. The blackest part of the cloud was the centre of its under or convex side, whence the cone descended. There soon appeared floating substances, both in the cone and cloud, which were mistaken by many persons for birds whirling about and carried along seemingly unable' to extricate themselves from the vortex. Among its first ravages was an orchard in Johnston, the trees of which were uprooted or broken, and the fences, and even stone walls, were swept away. Passing along over the summit of a hill or ledge of rocks one hundred feet high, it overthrew and demolished a small powder-house, containing thirty kegs of powder used in blasting, and neither the kegs nor their contents have ever been found. Near

this it uprooted a solitary large tree, and carried it twenty or thirty yards, to a valley at the farther side of the hill. Near this it unroofed two barns, a workshop, and a dwelling-house. All the doors of the house were burst open outwardly. A female standing in the middle of a room was hurled out of the door, and carried in a line with the progressive tornado across the road, and lodged against a fence. A wagon standing near was lifted and carried some distance. The approach of a whirlwind was apprehended by a workman in the shop, before it had struck, from the falling of a shower of apples on the roof, which it seems had been carried into the air from the orchard it had passed through, and which were precipitated from the anterior edge of the cloud. In a few seconds the pendant cone reached the shop, and unroofed it. A few rods farther in its progress, it took two women from a cart and carried them into a field. A few rods onward, it was seen approaching by a man who was leading a child, and fearing it would separate them, he clasped the child in his arms and fell on the ground; but they were both raised and borne for several yards. Passing through a potato-field, it dug up the potatoes, and scattered them far and wide. A small pond that lay in its path was drained; and, coursing through a large nursery-garden, it laid the shrubs and small trees. as flat as if done by a roller, uprooted or fractured the large trees, and despoiled them of their foliage. An apple-orchard near by was served in like manner. Its approach being now discovered by a school-teacher, from a chamber window, she hastened her little scholars from the chamber, which was over a back kitchen, into the main building, which they had barely reached when a dairy-house was raised in the air and thrown on the school-room, breaking through its roof. It then passed over a bleachery, and destroyed a row of buildings, whose roofs appeared to open, and in a moment to rise up in the air. The whole house,' says Mr. Allen, who was within a few fathoms, appeared to crumble, and to become a mass of ruins in motion, which one could see through the cloud which enveloped it as a cloak of vapor. At the moment when the lower extremity of the cone passed over the crumbling building, all the débris appeared to be shot into the air, as if from an exploded mine.' The noise resembled that of the letting off of steam from an engine, only not so cavernous.

"The tornado had now reached the shore of Narraganset Bay, in crossing which it presented to view a water instead of a land spout, and established their essential identity in the minds of any who doubted.

In passing land, loose substances, as the débris of trees and buildings, are raised; in passing water, vapor and spray are raised, as in the ocean-spouts, by one and the same power. The shape of the lower cone is, however, better defined and more uniform in the water than in the land spout, the supply of materials to form the latter being more variable on land. There is, however, an exception to this, when the land-spout passes over desert sands, which give the appearance of moving pillars of dust extending from the earth to the skies. Bruce, in his travels, describes them as tall pillars, and says he sometimes saw many of them travelling together.

"The materials raised on the land were precipitated from the cloud before it had passed half way across the water, and on the opposite side it began to raise other movable substances. The water over which it passed was thrown into violent ebullition, like an immense cauldron, giving off a dense vapor and spray from its surface over an area of three hundred feet in diameter. A flash of light or electricity was seen by two observers darting through the cone, which was followed by a lessened commotion of the water, and a fall of rain. The track of the tornado was two to three hundred feet wide, deviating little if any from this width for several miles, its limits being strongly marked on the ground and upon trees. Even the same tree, that stood on the margin of the track, had its trunk killed, the sap being dried, as it were, on one side, and not on the other. Peltier describes similar effects from a spout in Fontenay, where the side of trees af. fected by the meteor was dried, while the opposite side preserved the sap.' The diameter of the shaft or cone, midway between the cloud and earth, was apparently less than fifty feet.

"The length of the visible cone that shot down from the cloud va ried every minute. Sometimes it seemed to elongate in a tapering form quite to the earth, and then to shorten again. This, of course, was an optical illusion, for there is no descent of the spout in such cases, but merely a condensation of vapor, whose particles are constantly ascending, whether visible or not. And were the condensation of vapor to descend as far and wide upon the earth as the dynamic effects of the tornado extend, we should see the form of the terrestrial cone shooting upward to meet the descending inverted cone, they would be continuous from the earth upward; and this, in fact, is exhibited in water-spouts, the water supplying the vapor to make a continuous visible spout, extending from its surface into the cloud, which slightly resembles in form an astral lamp.

"I took Professor Espy to view the ground soon after the tornado had passed, who drew my attention to the position of trees that were prostrated, and which lay with their tops turned inward and forward. He explained this in accordance with his published theory, which maintains that the dynamic effects upon the trees are of two kinds, one resulting from the inward and vertical attraction, produced by a vacuum in the cloud, drawing the trees inward toward the cone, and upward, and uprooting them; the other, from its progressive course, which fells them with their tops forward. He states in his book that in nine spouts he has visited in New Jersey, the trees and corn all exhibited an inward and forward direction. He attaches less importance to the gyratory motion than Read, Redfield, and others have done, and believes it to be accidental. And Dr. A. D. Bache, of Philadelphia, who accompanied Professor Espy in some of his examinations of the traces of a spout, says: -'I think it made out that there was a rush of air from all directions, at the surface of the ground, toward the moving meteor, this rush of air carrying objects with it. The effects all indicate a moving column of rarefied air, without any whirling motion near the surface of the earth.' In support of the same opinion, I may mention that the roofs of the barns and the wagons in the Providence tornado were lifted upwards, and carried along in a straight line, without being whirled round. Although the electrical ef fects attendant upon water-spouts and whirlwinds prove that they are closely connected with atmospheric electricity, yet no theory has been advanced that satisfactorily explains all the phenomena. Peltier has given the most rational exposition of the modus operandi of electricity of any writer I have met with. He has attempted to illustrate it by artificial means and experiments, and with apparent success. On this point Espy differs from him, in referring the dynamic effects of spouts chiefly, if not wholly, to a vacuum in the cloud, which he seems to believe may exist independently of electricity. It is, however, improbable that any rush of air, unaided by electricity, can produce a drying up of the leaves and of the sap in a tree. The electric fluid, moreover, is often seen darting through such meteors, as was the case in the spout now described."

Professor Edward Salisbury, of Yale College, and Dr. J. Mason Warren, were elected Fellows of the Academy.

Three hundred and twelfth meeting.

November 14, 1848. MONTHLY MEETING.

The PRESIDENT in the chair.

Colonel Graham, of the U. S. Topographical Engineers, gave an account of the labors of the commissioners for running the boundary between the United States and Canada, as established by the Treaty of Washington, and stated that the maps, which were destroyed by fire at Washington when nearly completed, were now in course of reconstruction from the field-notes, &c., copies of which, by direction of the government, were deposited in different places, so as to guard against their destruction by fire, or other casualty.

Professor Webster exhibited remarkably fine specimens of beryl from Royalton, and idocrase from Sanford, near Wells, Maine.

Mr. Desor made some remarks on the retrogression of Niagara Falls, illustrated by plans, and gave reasons for believing that, in their future retrogression, the gradual diminution in the height of the cataract which has been taught by other geologists would not take place.

Professor Lovering read a paper on the causes of the remarkable differences in the strength of ordinary magnets and electro-magnets of the same shape and size, as follows:

"It is well known that the strength of ordinary magnets does not increase in the same proportion as their weight; but much more slowly. For example, a magnet weighing only three grains has lifted two hundred and fifty times its own weight. A magnet weighing twenty-five grains sometimes lifts forty-five times its own weight. Peschel's new method of magnetizing is considered very efficient, because it will give to a magnet which weighs one pound the power to lift about twenty-six pounds. Magnets of two pounds' weight will rarely lift ten times their own weight. A magnet in the possession of Mr. Peale, of Philadelphia, (the largest natural magnet known,) weighs fifty-two pounds and lifts three hundred and ten pounds; that is, only six times its own weight. These cases are not strictly comparable, because the shape and quality of the iron are not the same in all of them. They indi