Elliptical Form Research Articles

On the Remarkable Form of Hailstones

WITH reference to the description given in NATURE (vol. xl. pp. 151 and 272) of the hailstorm at Liverpool, it will probably be interesting to bring under notice an early account of the remarkable forms often possessed by hailstones; it is to be found in the Edinburgh Philosophical Journal for 1824, vol. xi. p. 326. The writer of the said article states that “in the second part of the eleventh volume of the ’Nova Acta Physico-Medica Academiæ Cæsareæ Leopoldinæ Carolinæ Naturæ Curiosorum,’ Dr. Nögerath informs us, that, on May 7, 1822, a tremendous hail-shower fell in and around Bonn.... The general size of the hailstones was about one inch and a half in diameter, with a weight of nearly 300 grains. When whole, which was not generally the case, the general outline was elliptical or compressed globular, and the form cerebral, or resembling the brain of a warm-blooded animal.... More frequently the form was lenticular, and appeared polished on the two ends, as if by friction. The masses had a concentric lamellar structure; in the centre was a white, nearly opaque, nucleus, of a round or elliptical form, around which were arranged concentric layers, which increased in translucency from the innermost to the outermost. They at the same time exhibited a beautiful stellular fibrous arrangement, caused by rows of air-bubbles disposed in radii.... Captain Delcross, in the thirteenth volume of the ’Bibliothéque Universelle,’ describes hailstones having the concentric lamellar structure and stellular fibrous arrangement.… The surface was provided with pyramidal forms.... When the edges and the angles of the pyramids are melted down, the cerebral form is produced; when the masses of hail, having the structures described, burst asunder, the fragments have a pyramidal form, and then forms what has been described under the name of pyramidal hail.” The writer then proceeds to describe hailstones which fell on June 27, 1823, at Aberdeen. “They (the hailstones) were included, almost universally, each by five sides or surfaces, four plane, constituting the sides of an irregular pyramid, and one spherical in place of a base.... The spherical surface appeared, to the depth of one-twentieth or one-thirtieth of an inch, to be solid as it was transparent. The rest of the hailstone was opaque, consisting of crystals or minute columnar forms, perpendicular to the spherical surface.” Eight figures, illustrative of the different kinds of hailstones, are given (Plate ix.).

Landslips.—The Cheshire Subsidences

UNDER the guidance of Mr. Thos. Higgin, F.L.S., and your correspondent Mr. Ward, I have just been examining the subsidences that have been lately taking place in the neighbourhood of Northwich. To understand how they occur, it is necessary to know that there are two beds of rock salt in the Triassic marl. The upper bed, 25 yards thick, is from 40 to 60 yards below the surface; the lower, 35 yards thick, is separated from the upper by about 10 yards of hard marl. The greater bulk of the salt is obtained in the form of brine pumped up from the upper bed. The lower bed is to a smaller extent worked as a salt-mine. From these operations two classes of subsidences result: the one general and gradual, due to the removal in solution of the rock salt of the upper bed by percolation of water and pumping, by which the surface of the ground sinks in undulations; the other, sudden fallings in of the ground into the mines, forming crater-like pits. It is to these I wish to call attention. I was fortunate enough to see one before it had become, as they all do, partially filled with water. I should judge it to be about 70 feet deep, 150 feet diameter at the top, and 20 or 30 feet at the bottom, where a little water was lodging. The problem to account for is how such an inverted cone of marl capped with boulder-clay and drift-sand could apparently have disappeared through so small a hole? The explanation appears to be this: By percolation of water the roof of the mine begins locally to give way and fall into the mine, gradually working its way to the surface, where it first appears in the form of a hole about the size of a well. The vacuity will no doubt take a conical form, the base being at the roof of the mine; once the hole is formed, the surface-ground begins to slip and fall in around, gradually enlarging the orifice, the material disappearing into the mine below. This continues until the bottom is filled up and the sides of the “crater” attain the angle of repose. The whole thing will occur in a night. The subsidences certainly present a very remarkable appearance from the regularity of their circular or elliptical form and funnel crater-like shape. It is evident such subsidences could not happen except under special conditions, such as are provided by salt-mining and pumping in these Keuper marls.

The Zodiacal Light

MR. BACKHOUSE asks if the observations given in vol. iii. p. 203, afford any proof that the Zodiacal Light is not a lens-shaped disc of light enveloping the Sun; if this theory were correct, and the sun enveloped in a continuous mass of light-reflecting matter, whenever the light is seen in the evening after sunset, it ought to be also seen in the morning before sunrise, of the same brilliancy at the same angular distances from the sun, especially when those distances are small, for then the effect of an elliptical form in the section of the envelope by the plane of the ecliptic would be almost entirely eliminated.

II.—On a Sudden Sinking of the Soil in a Field at Lexden in Essex

In the month of May, 1861, there occurred a curious subsidence of the soil in a field on the ‘Malting Farm’ at Lexden in Essex. The cavity thus produced was about twenty-five yards in circumference, of an elliptical form, and about twenty feet in depth, with the sides slightly overhanging. The subsidence took place quite suddenly; some workmen, who were in the field in the forenoon, finding the pit fresh formed on their return from dinner. The ground in which the pit is situated consists of a slightly rising bank of valley-gravel, and is about fifty yards to the south of the little River Colne, which runs past the spot, and gives its name to the ancient town of Colchester. The surface of the field cannot be more than five or six feet above the stream when full.

On the Occurrence of Obsidian Bombs in the Auriferous Alluvia of New South Wales

I n Mr. Darwin's ‘Geological Observations on the Volcanic Islands visited during the voyage of H.M.S. Beagle’ (p. 38), that author describes and figures a volcanic bomb of green obsidian from the plain between the Rivers Darling and Murray, and which he received from Sir T. L. Mitchell. The explanation given by Mr. Darwin appears to be satisfactory as to the origin of that individual specimen, and it is confirmed by the parallel examples cited from M. Beudant. Sir T. L. Mitchell's specimen would seem either to have been drifted from a very long distance, or, which is more likely, from the known habits of the aboriginals, to have been dropped by one of them, who probably found it in the trap-hills of the Lachlan to the north-eastward. This specimen was unique as to Australia, until recently. During the last two years, several similar specimens have been found in the auriferous detritus of the western and northern Goldfields. The first which I met with was found in the cradle of a gold-washer on the Turon River, who dug it from a depth of 30 feet below the surface. This was a small, irregular, roundish substance, 0·6 inch in diameter, having a specific gravity of 2·7 at a temperature of 66°. It was undivided, and more like those examples described by M. Beudant than tile figure given by Mr. Darwin. A similar specimen, but of a rude elliptical form, ½ inch diameter in the major axis, and having a sp. gr. of

On the aurora borealis which occurred on the evening of Friday, the 17th of November, 1848

The author states that the 17th of November was a fine day with a clear sky and bright sunshine: towards evening the sky became cloudy and a few drops of rain fell, but it soon again became clear, with the exception of a few fleecy clouds that here and there dimmed its brightness. At 6 h 45 m a soft and gentle light began to illumine the northern region of the sky; and at 7 o’clock a considerable portion of it was covered with dark-red streams of light towards the east; while streamers moving to and fro, arrayed in colours of golden and silvery hues, overspread the south and north. About 8 o’clock there appeared near the zenith, and upon the magnetic meridian, a ring of an elliptical form, from which proceeded in all directions towards the horizon, beams or columns of light, giving to the heavens the appearance of a splendid vault, with its top adorned with a crown or wreath; while around and within the vault were to be seen clouds of brilliant light flashing towards and from the crown or central circle of the aurora, sometimes tinged with prismatic rays, at other times intensely white and lucid. About half-past nine nearly the whole of the aerial canopy was clad with clouds of a bright red colour, casting a curious reddened hue over the objects on the surface of the earth. After a short period of time had elapsed, the red colour began to diminish in intensity, and was again replaced by the white dome. However, in various parts of the sky the red colour still remained, principally in the north-west, southwest, and north-east. Between the hours of twelve and one beams of brilliant white light commenced shooting up in the south from the horizon to the central ring or pole. The beams appeared to be at nearly equal distances from each other, the entire column of them stretching over a space equal to about one-fifth part of the visible horizon, in the form of a fan. The whole figure rapidly changed from a pure white light into a glow of brilliant colours of every tint, variegating the undulating waves as they rolled on their way to the pole of the aurora. In the course of three minutes these gave place to the white flashing radiations. During the time of the aurora there were a great number of small meteors, the direction of whose motion was from east to west, and which appeared to be considerably below the sphere of the aurora.

II. The Bakerian Lecture. Observations upon an unusual hori­zontal refraction of the air ; with remarks on the varia­tions to which the lower parts of the atmosphere are sometimes subject

The uncertainty of the refraction of the air near the horizon has long been known to astronomers, the mean refraction varying by quantities which cannot be accounted for from the variations of the barometer and thermometer ; on which ac­count, altitudes of the heavenly bodies which are not more than 5° or 6°, ought never to be made use of when any consequences are to be deduced from them. The cause of this uncertainty is probably the great quantities of gross vapours, and exhalations of various kinds, which are sus­pended in the air near to the earth’s surface, and the variations to which they are subject ; causes, of which we have no instru­ments to measure the effects which they produce, in refracting the rays of light. In general, the course of a ray passing through the atmosphere, is that of a curve which is concave towards the earth, the effect of which is to give an apparent elevation to the object ; and thus the heavenly bodies appear above the horizon, when they are actually below it; but it will not alter the position of their parts, in respect to the horizon, that is, the image of the highest part of the object will be up­permost, and the image of the lowest part will be undermost. The figures, however, of the sun and moon, when near the horizon, will suffer a change, in consequence of the refraction of the under limb being greater than that of the upper ; from which they assume an elliptical form, the minor axis of which is perpendicular to the horizon, and the major axis parallel to it. But a perpendicular object, situated upon the surface of the earth, will not have its length altered by refraction, the refrac­tion of the bottom being the same as that of the top.* These are the effects which arc produced upon bodies at or near the horizon, in the common state of the atmosphere, by what I shall call the usual refraction. But, besides the usual refraction which affects the rays of light, the atmosphere over the sea is sometimes found to be in a state which refracts the rays in such a manner as to produce other images of the object, which we will call an effect, from an unusual refraction. In the Phil. Trans, for 1797, Mr. Huddart has described some effects of this kind, which he has ac­counted for by supposing that, from the evaporation of the water, the refractive power of the air is not greatest at the sur­face of the sea, but at some distance above it; and this will solve, in a very satisfactory manner, all the phenomena which he has observed. But effects very different from those which have been described by Mr. Huddart are sometimes found to take place. These I had an opportunity of observing at Rams­ gate, last summer, on August the first, from about half an hour after four o’clock in the afternoon till between seven and eight. The day had been extremely hot, and the evening was very sultry; the sky was clear, with a few flying clouds. I shall describe the phenomena as I observed them with a terrestrial telescope, which magnified between 30 and 40 times ; they were visible, however, to the naked eye. The height of the eye, above the surface of the water, at which most of the obser­vations were made, was about 25 feet; some of them, however, were made at about 80 feet from the surface ; and it did not appear that any of the phenomena were altered from varying the height of the eye, the general effect remaining the same.