broken, being mostly under cultivation and with few trees exposed to the tornado, excepting an orchard of scattered apple trees westward of Tifts' house. The traces of the wind in and adjacent to this orchard were very distinct in their character, and I subjoin here the sketch on which they are represented.

EXPLANATIONS OF FIG. III.-The cases of prostration 4 to 14, were from a line of small locust trees on the west border of an old apple orchard, and are severally shifted a little out of line for the sake of a distinct exhibition of their directions.

From thence to near Tifts' house at b, the ground is but slightly foreshortened, and the relative positions of each tree, on the left of the centre, is approximately shown. The figure was drawn from my field notes on account of the distinct phenomena which were exhibited on this part of the track, and which, in cases a, 14, 22, 21, 23, and 27, show conclusively the first action of the whirl across the path of the axis, and sweeping towards the northern border of the track. On the opposite or right side of the axis, southward of 15, there were no trees exposed, and the effects of the tornado were here visible only on the crops and fences. Therefore the cases shown on the figure south of the axis, and also westward of 22 on the left hand side, were brought in from the more western parts of the track between the orchard and the river, and include all the prostrations from the latter to Tifts' house;

22

and their relative distances from the axis or centre of the track are

but approximated.

Case 14, represents a small locust tree broken off at an old wound near the root and carried outward and backward into the adjoining fallow field, having struck into the ground several times in its course, leaving distinct traces. It was finally left at a point N. 57° W. from its stump, at the distance of forty yards, with its top turned southwardly, in conformity with its two last traces in the soft ground.

Case 10, a small locust tree was prostrated S. 25° W., leaving its mark in the fallow ground. It was subsequently shifted, by the progressive change in the whirlwind, to S. 11° E.

Case a, an old apple tree with but a single branch projecting southwardly from its trunk: This branch was taken off by the onset of the tornado, and struck into the ground northwest from the trunk, depositing its apples at this spot. The limb itself was missing.-Case 21, apples deposited as in case a.

Case 22, a small wild cherry tree, was found lying on and against the stump of 14, having first been thrown from the latter by the onset of the wind and subsequently swung round by the south to its present position, as appeared by the impressions made in the ground. Its final position was such, as if occurring at the outset would have prevented 14 from being carried off northwesterly.-Case 23, the branch of an apple tree was thrown west.-At b is shown the relative position of Tifts' house.

Case 27, shows the original position of a large pear tree, the stem of which was broken off and first thrown northward, where it ploughed up the soft ground of the garden by its force, and continued its circuit to a point northwest of its original position, where it remained with its top turned toward the south.

For the purposes of a general comparison, the observed or first known directions of the prostrations on the two sides of the track may be summed up as follows.

Left or North side of the Track.. Right or South side of the Track.

Direction of first prostraCase. tion.

11 S. 26° E.

tornado.

Inclination inward and Mean direction of prostration on backward from course of the right side of the track N. 73° E.: 64 degr's. average inclination inward from course of tornado, seventeen degrees.

35

12 S. 55 E.

13 S. 55 E.

35

Mean direction of first prostrations on the left side of track, S. 4° W.: average inclination inward and backward from course of tornado, ninety-four degrees.

Relative inclinations of the two sides to the line of axis, more than five to one.

It is proper to mention, that the average inward inclination of all the prostrations on the right side of the track for a distance of four miles east of the river was thirty degrees. This, however, does not affect the conclusions in favor of rotation to the left.

*

These average results, on the two sides, together with the several particular observations already adduced, appear to me to afford decisive evidence of whirlwind rotation in this tornado, in the direction from right to left or which is contrary to the hands of a watch. In reference to this evidence and that exhibited in my paper on the New Brunswick tornado, I add from my prepared sketches the following figure, as an approximate illustration of the whirling action in these tornadoes, so far as this may be shown horizontally and by a stationary figure.

Let the involuted lines or arrows on figure IV be supposed to represent the motion of the wind at or near the bottom of a vertically cylindrical portion of the centre of a tornado, comprising a length of radius equal to the greatest width of the prostrating power on the right of the axis of its path. Now if the tornado be considered as whirling in the manner here represented, but without any change of location, its action may be supposed as concentrically equal on all sides; the motion, however, becoming quickened towards the centre in the inverse ratio of the successive concentric areas: that is, each. particle of air as it revolves about the axis, continuing to describe nearly equal areas in equal times, in its progress towards the centre, where it rises spirally in the direction of discharge; this direction being vertically at the centre, the point or area of least atmospheric resistance or pressure. Thus, the course of a single particle, horizontally, may be a b

This larger average gives a relative degree of inclination on the two sides of three to one.. Nearly the same difference is found in two outside bands of prostration, of equal widths,. (Tables I and V,) shown in my survey of the New Brunswick Tornado. See this Journal, vol. ii, 3rd series, 1841, p. 44.

cdefghik;-and so on or between each of the four involuted lines which constitute the figure.

For further reference, we may divide this figure by the cross lines of arrow heads, into the four quadrants 1, 2, 3, 4.

We will now consider this whirl as having a constant progressive motion on the line of the long arrow c c, at a rate equal to one-fourth or fifth of its average rotative velocity. It will then foliow, that as the force of the whirl on the trees and other objects encountered by it, is as the square of the wind's velocity at the point of impingement, the relative effects on the two sides of the line of the axis, which before were equal, will now be greatly altered.

For, if at a given distance on the right of the advancing axis, the former velocity was 80, it will now, as relates to the earth's surface, have become 100; and at the same distance on the left side the velocity of the wind will be reduced to 60, as relates to the earth's surface. Thus the squares of these effective velocities will give a power relatively equal to 100 at the former point and only 36 at the latter; both being equally distant from the axis. Hence, although the rotative velocity of the whirl decreases rapidly as we recede from its axis, yet its prostrating power will, by its progressive motion, become greatly extended on the right side of the advancing axis, and proportionally contracted on the left side. Thus the respective boundaries of the prostrating power on the two sides of the tornado, when thus in mo

tion, may be those indicated on the figure; which nearly correspond to the effects which have been observed in several cases.

It may be seen further, that nearly all the prostrations near the line of the axis and elsewhere, must by the advancing motion of the tornado, receive a direction more onward than is represented by the arrows or lines in the figure, which can represent only a stationary rotation. In further considering these effects, in different portions of the whirl, as it encounters objects in its advance, we shall find the maximum effects to be mainly on the line a, i, o, at the rear of the first quadrant. Hence, if a tree on this side the axis should fail to be prostrated till after the first quadrant had passed over, it would not be likely to fall in the fourth quadrant, on the further advance of the tornado, unless very near to its axis. Moreover, if one tree should fall when under the more advanced portion of the first quadrant, another if prostrated later in the same quadrant, must necessarily fall in a more onward direction than the first, and if sufficiently near will lie across the latter.

It may likewise be seen, that the wind of the whirl in passing into the second quadrant, on the left side of the track, is sweeping backward, and with its effective power thus greatly reduced, as regards fixed objects on the earth's surface. Thus the limits of prostration are not only narrowed, but the effective power is here greatly reduced, and gives fewer prostrations than under either the first or third quadrants. The minimum of effect occurs on the arrival of the line e k, at the rear of the second quadrant.

But on the arrival of the third quadrant, the prostrating power on the left side becomes more and more efficient by the ceasing of the backward and the accession of the progressive movement; and at or near the line of ƒ m, it again takes effect, with rapid increase. The destructive force is also much augmented here by the greater velocity in the heart of the whirl, near its axis, and the impetus must rapidly incease in energy to its maximum effect, as at m n o, taking off any tree which may here remain, and carrying aloft, or sweeping onward, the objects previously prostrated on the line c x k.

If a tree on the left side of the track falls on one previously thrown down by the tornado, the last fallen will also have the more onward direction, as on the other side: unless both have fallen in the second quadrant, where few prostrations occur. The fourth quadrant, for causes noticed in considering the first, can have little prostrating effect; except perhaps on the small area near its axis.

If we now conceive of our figure as applied only to the limits of prostration or destruction which constitute the visible path of the tornado, it becomes apparently and relatively unequal, in its right and left hand quadrants, the axis appearing greatly eccentric, and in the same degree, at least, as the left band or belt of prostrations is found narrower than that on the right of the axis. This apparent, but illusive form of the whirl, may be illustrated by Fig. V, which is drawn on the same lines with the preceding figure.

It will readily be seen that this eccentricity of the axis, on the visible track, will be in proportion to the progressive velocity of the tornado; other things being equal. Thus, if Mr. Allen be nearly right