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veracity, and who must have had plenty of opportunities of studying their habits (having lived upon them for some time whilst on the west coast), assures me that they never use any other mode of progression than that I have described, viz., using their head as third foot, as it were ; much in the same way as we see the common parrots use their bill as a third foot in climbing. It is entirely a ground bird, and is singularly like an owl, on account of the feathers radiating away from the eyes, as in the owl tribe.”
Mr. WALKER exhibited a number of animals collected from the Gulf-weed during his homeward voyage, consisting of specimens of Pipe-fish (Syngnathus), Painted Hand fish, or Toad-fish (Cheironectes), several Crustaceans and Velelle ; two small Cephalopods ; two Nudibranchs and an Acaleph, which he presented to the museum.
EXPERIMENTS WITH ROTATING DISCS.
Mr. ALFRED HIGGINSON exhibited some Experiments with Rotating Discs, and made the following observations :
Any body, even of irregular form, when made to rotate rapidly, will (if free to do so) arrange itself in such position as to spin round its shortest axis ; that axis moreover passing through its centre of gravity ;-and, if the rapid motion could be sustained, would show the various phenomena of gyration. The regular form of an oblate spheroid, or a disc with thickened margin, is however, the most convenient figure. Such a body when supported, and spinning, on its very centre of gravity, will not of itself change the direction of its axis, or its plane of rotation; but will resist any effort to change it by a force applied from without. This may be called the balanced top, the centre of gravity and centre of motion coinciding; and the top, when spinning or not spinning, will rest at any inclination at which it is placed.
When the centre of gravity is below that of motion or support, the top when at rest will always assume a perpendicular position of its axis. This may be called the under-balance top.
When the centre of gravity, however, is above that of support or motion, the top when not spinning will fall over, and may be called the over-balanced top.
Mr. HIGGINSON exhibited an instrument, invented by himself about the year 1829, capable (in its present more accurate form) of spinning for fifteen minutes, and in which these three different adjustments of centre of gravity and centre of motion can be made at will.
1. The over-balanced condition was shown to correspond to the familiar toys, peg-top, whip-top, humming-top and teetotum. When rotating with the axis inclined, it was shown that a gyration takes place in the same direction as the revolution of the disc, and the toys named move also in an orbit in the same direction when travelling on the floor or table.
2. The under-balanced adjustment corresponds to the real condition of the earth in its diurnal rotation on its axis; but the gyration is in each instance in a direction the reverse of its rotation; and is, in the case of our globe, the cause of the precession of the equinoxes.
3. The balanced state of Mr. H.'s instrument is identical with the condition of the Gyroscope, when well made and not subjected to extra weight and pressure from without; and the experimenter believed that many of its seemingly capricious movements were explicable on the principle of the sudden conversion of the disc of the Gyroscope from the over-balanced to the under-balanced top, or vice-versâ, with their distinct and opposite gyrations. These gyrations themselves are easily intelligible on physical principles relative to the action of two or more forces.
In the balanced top, when spinning in an oblique position, each particle at the equator will be carried from one node to the exact opposite, and there will be no alteration in the direction of the axis of rotation; while in the over-balanced, the node will be carried forward in the same direction as the spinning, and in the under-balanced the node will be thrown back in a direction the reverse of the spinning. In each case, the obliquity of the axis is not changed; but in the one it revolves at the same angle in the direction of, and in the other opposed to, the spinning of the top.
Spin the Gyroscope (with double gynbals,) and when the axis is vertical it will admit of being pushed round horizontally with perfect ease in the same direction as its rotation, but resists completely an impulse in the opposite direction, until the disc has turned itself upside down; the rotation is then in harmony with the impulse, and it will turn without difficulty ; reverse the impulse, and it will not move round until the disc has reversed itself. Couple the two rings of the Gyroscope firmly together and it will then turn freely in either direction, without reversing its poles. When free to move, it was the over-balanced top, and it acted accordingly. Now place the axis horizontally, and with a thread attempt to raise one pole; gyration will ensue in a direction opposite to the rotation ;-it is the under-balanced top, in all essential conditions. A weight bung at the other end of the axis produces the same effect as the thread in this experiment.
Mr. Higginson expressed the hope that any member of the Society, who might not be at once convinced of the validity of his statements, would yet feel sufficient interest to follow up this curious subject with investigations of his own.
The following paper was then read
DETONATING METEOR OF DECEMBER 5TH,
By ALEXANDER S. HERSCHEL, Esq.
(Communicated by F. J. Bailey, Esq.)
Meteors of the detonating class are rare and their occurrence deserves a more careful consideration than a cursory notice of their appearance in the columns of the daily newspapers can supply. Professor Heis, director of the Royal Prussian Observatory at Münster, set an excellent example to Meteorologists in the early part of last year, by the personal enquiries which he undertook and completed upon the track of the meteor of March 4th, 1863, in the southern part of Holland. This great meteor offered small difficulties to an astronomer of Professor Heis' experience, from the length and small inclination of the visible path by which it approached the earth. Many distant places contributed their observations, by which the beginning and end of the rectilinear flight could be determined with precision, and hence it was possible to infer that the luminous body was foreign to our solar system and came from the trackless region of the stars.
The occurrence which now demands our attention is that of a detonating meteor in England, on the 5th December last. Mr. R. S. Hart writes on the subject to “The Times," from Hawkshead, Windermere, as follows :-" The evening was calm and clear. From four to five minutes after the disappearance of the meteor a distant rumbling sound, which continued for two or three seconds, and resembled that arising from a railway train passing over a bridge, was distinctly heard by myself and others. It came from the south-west, the direction towards which the meteor seemed to fall. Although the circumstance has not been alluded to by any of your correspondents, there was no doubt entertained by those who heard the sound, that it was occasioned by the meteor.” It is sufficient to awaken our interest in this astronomical occurrence to be assured that a body so near the confines of empty space as to light the whole of England with a flash like lightning should be perceptible to our restricted and material sense of hearing. What then were our more ethereal organs of perception able to witness of the event ?
We may recall the appearance which the meteor presented at Liverpool, at Oldham (Manchester), at Burton-upon-Trent, at Preston and other places.
Mr. W. G. Drysdale writes—" It at first assumed the form of a falling star, and such I took it to be, until after descending several degrees, it suddenly burst forth into a large blue light, so brilliant as to cast shadows from objects on the earth. As this light was fading, a drop or pendant, of a dull red colour ran down from it and terminated in a small explosion. The diagram represents the image left on my mind after the disappearance of the whole.” (Fig. 1.)
Mr. W. Bentley writes from Oldham—“At the time of its maximum brilliancy it was as light as the finest moonlight night. At the commencement it was as a ball of fire of one. third the apparent diameter of the moon, and of a lemon-shape and brightest at the lowest point. It proceeded some distance, leaving in its track a band of fire of a bluish white colour, when a very bright jet of fire was projected from the lowest part of the ball some distance. The whole of the ball was instantly a mass of fire, of the most brilliant kind, surrounded especially on the upper side with a vivid blue flame, and became suddenly extinguished, leaving a band of red flame which appeared to be cut in two at the point where the ball was.”