though somewhat confused, was as yet unbroken. Once, if not twice, William was driven back and put in imminent danger by the Irish horse and the French troops of Lauzun; but the Enniskilleners performed most manfully, Schomberg's horse came up, General Ginckel made some brilliant charges; and, in the end, James's army was beaten, right, left, and centre, and pushed off the field. The fleeing James got to Dublin' that night, but he no longer considered himself safe there, and, travelling all night, he got to Duncannon about sunrise, and there embarked for France. Attempts have been made to give a different colouring to his conduct; but a cool examination of facts enforces the impression that he really ended as a coward the enterprise which he had begun and conducted like a fool. The poor Irish, smarting under defeat, and forgetting other considerations, said, with some humour, that if the English would only change kings with them, they would be glad to. fight the battle of the Boyne over again. They and their French allies had lost about 1,500 men in the battle and retreat, and among them some persons of note, as Lord Dangan, the Earl of Carlingford, Fitzgerald, Sir Neal O'Neal, the Marquis d'Hoquincour, Colonel Casanova, &c. Driven from the Boyne, they resolved to make a stand on the Shannon, where the standard of James still floated over the strong walls of Athlone and Limerick. Drogheda, at the mouth of the Boyne, surrendered the day after the victory, and on July 3, the Duke of Ormond, with nine troops of horse, secured Dublin for King William, who, on the 4th, marched that way with his whole army, and on the 8th rode in a triumphant manner into that capital, where the Protestants, and for the same sort of reasons, were as joyful as the Papists had been the year before at the arrival of King James. He went directly to the cathedral church of St. Patrick, now again restored to the Protestant faith, and returned thanks for his victory. MENSURATION. To find the area of a circle: (1) Find the area of a circle whose diameter is 40. (2) What is the area of a circle whose circumference is 9.2? (3) What is the area of a semicircle whose diameter is 200? (4) Find the area of a quadrant whose radius is 10 feet. What must be the length of a cord fastened to a cow's horn at one end, and a stake at the other, to enable it to feed on two acres of land, and no more? (6) In running a surveying wheel round the edge of a circular pond, it turns 455 times. Now, the circumference of the wheel is 8 ft. 3 in. What is the area of the pond? AURORA BOREALIS. (From Cosmos,' by A. Von Humboldt.) zen'-ith, the point of the heavens imme-en-gen'-der, to produce, to cause diately overhead si-mul-ta'-ne-ous, existing or happening at the same time pre-mon'-i-to-ry, giving previous warn- dy-nam'-ics, the science of force ho'-ra-ry, relating to an hour TERRESTRIAL magnetism, and the electro-dynamic forces computed by the intellectual Ampère, stand in simultaneous and intimate connection with the terrestrial or polar light, as well as with the internal and external heat of our planet, whose magnetic poles may be considered as the poles of cold. The bold conjecture hazarded one hundred and twenty-eight years since by Halley, that the aurora borealis was a magnetic phenomenon, has acquired empirical certainty from Faraday's brilliant discovery of the evolution of light by magnetic forces. The northern light is preceded by premonitory signs. Thus in the morning before the occurrence of the phenomenon, the irregular horary course of the magnetic needle generally indicates a disturbance of the equilibrium in the distribution of terrestrial magnetism. When this disturbance attains a great degree of intensity, the equilibrium of the distribution is restored by a discharge attended by a development of light. 'The aurora itself is therefore not to be regarded as an externally manifested cause of this disturbance, but rather as a result of telluric activity, manifested on the one side by the appearance of the light, and on the other by the vibrations of the magnetic needle.' The splendid appearance of coloured polar light is the act of discharge, the termination of a magnetic storm, as in an electrical storm, a development of light-the flash of lightning-indicates the restoration of the disturbed equilibrium in the distribution of the electricity. An electric storm is generally confined to a small space, beyond the limits of which the condition of the atmospheric electricity remains unchanged. A magnetic storm, on the other hand, shows its influence on the course of the needle over large portions of continents, and, as Arago first discovered, far from the spot where the evolution of light was visible. It is not improbable that as heavily-charged threatening clouds, owing to frequent transitions of the atmospheric electricity to an opposite condition, are not always discharged accompanied by lightning; so likewise magnetic storms may occasion far extending disturbances in the horary course of the needle, with out there being any positive necessity that the equilibrium of the distribution should be restored by explosion or by the passage of luminous effusions from one of the poles to the equator, or from pole to pole. In collecting all the individual features of the phenomenon in one general picture, we must not omit to describe the origin and course of a perfectly developed aurora borealis. Low down in the distant horizon, about the part of the heavens which is intersected by the magnetic meridian, the sky which was previously clear is at once overcast. A dense wall or bank of cloud seems to rise gradually higher and higher till it attains an elevation of 8° or 10°. The colour of the dark segment passes into brown or violet; and stars are visible through the cloudy stratum, as when a dense smoke darkens the sky. A broad brightly luminous arch, first white, then yellow, encircles the dark segment; but as the brilliant arch appears subsequently to the smoky-grey segment, we cannot agree with Argelander in ascribing the latter to the effect of mere contrast with the bright luminous margin. The highest point of the arch of light is, according to accurate observations made on this subject, not generally in the magnetic meridian itself, but from 5° to 18° towards the direction of the magnetic declination of the place. In northern latitudes, in the immediate vicinity of the magnetic pole, the smoke-like conical segment appears less dark, and sometimes is not even seen. Where the horizontal force is the weakest, the middle of the luminous arch deviates the most from the magnetic meridian. The luminous arch remains sometimes for hours together flashing and kindling in ever-varying undulations, before rays and streamers emanate from it, and shoot up to the zenith. The more intense the discharges of the northern light, the more bright is the play of colours, through all the varying gradations from violet and bluish white to green and crimson. Even in ordinary electricity excited by friction the sparks are only coloured in cases where the explosion is very violent after great tension. The magnetic columns of flame rise either singly from the luminous arch, blended with black rays similar to thick smoke, or simultaneously in many opposite points of the horizon, uniting together, form a flickering sea of flame, whose brilliant beauty admits of no adequate description, as the luminous waves are every moment assuming new and varying forms. The intensity of this light is at times so great, that Lowenörn (on June 29, 1786) recognised the coruscation of the polar light in bright sunshine. Motion renders the phenomenon more visible. Round the point in the vault of heaven which corresponds to the direction of the inclination of the needle, the beams unite together to form the so-called corona, the crown of the northern light, which encircles the summit of the heavenly canopy with a milder radiance and unflickering emanations of light. It is only in rare instances that a perfect crown or circle is formed, but on its completion the phenomenon has invariably reached its maximum, and the radiations become less frequent, shorter, and more colourless. The crown and luminous arches break up, and the whole vault of heaven becomes covered with irregularly scattered, broad, faint, almost ashy-grey, luminous, immovable patches, which in their turn disappear, leaving nothing but a trace of the dark, smokelike segment on the horizon. There often remains nothing of the whole spectacle but a white, delicate cloud with feathery edges, or divided at equal distances into small roundish groups like cirro-cumuli. This connection of the polar light with the most cirrous clouds deserves special attention, because it shows that the electro-magnetic evolution is a part of the meteorological process. Terrestrial magnetism here manifests its influence on the atmosphere and on the condensation of aqueous vapour. The fleecy clouds seen in Iceland by Thienemann, and which he considered to have been the northern lights, have been seen in recent lines by Franklin and Richardson near the American North Pole; and by Admiral Wrangel on the Siberian coast of the Polar Sea. All remarked that the aurora flashed forth in the most vivid beams when masses of cirrous strata were hovering in the upper regions of the air, and when these were so thin that their presence could only be recognised by the formation of a halo round the moon.' These clouds sometimes range themselves, even by day, in a similar manner to the beams of the aurora, and then disturb the course of the magnetic needle in the same manner as the latter. On the morning after every distinct nocturnal aurora, the same superimposed strata of clouds have still been observed that had previously been luminous. The apparently converging polar zones (streaks of clouds in the direction of the magnetic meridian), which constantly occupied my attention during my journeys on the elevated plateaux of Mexico, and in northern Asia, belong probably to the same group of diurnal phenomena. Southern lights have often been seen in England by the intelligent and indefatigable observer, Dalton; and northern lights have been observed in the southern hemisphere as far as 45° latitude (as on the 14th of January 1831). On occasions that are by no means of rare occurrence, the equilibrium at both poles has been simultaneously disturbed. I have discovered with certainty that northern polar lights have been seen within the tropics in Mexico and Peru. We must distinguish between the sphere of simultaneous visibility of the phenomenon and the zones of the earth where it is seen almost nightly. Every observer no doubt sees a separate aurora of his own, as he sees a separate rainbow. A great portion of the earth simultaneously engenders these phenomena of emanations of light. Many nights may be instanced in which the phenomenon has been simultaneously observed in England and in Pennsylvania, in Rome and in Pekin. When it is stated that auroras diminish with the decrease of latitude, the latitude must be understood to be magnetic, and as measured by its distance from the magnetic pole. In Iceland, in Greenland, Newfoundland, on the shores of the Slave Lake, and at Fort Enterprise in Northern Canada, these lights appear almost every night at certain seasons of the year, celebrating with their flashing beams, according to the mode of expression common to the inhabitants of the Shetland Isles, 'A merry dance in heaven.' Whilst the aurora is a phenomenon of rare occurrence in Italy, it is frequently seen in the latitude of Philadelphia (39° 57′), owing to the southern position of the American magnetic pole. In the districts which are remarkable in the New Continent and the Siberian coasts for the frequent occurrence of this phenomenon, there are special regions or zones of longitude, in which the polar light is particularly bright and brilliant. The existence of local influences cannot therefore be denied in these cases. Wrangel saw the brilliancy diminish as he left the shores of the Polar Sea, about Nischnne-Kolymsk. The observations made in the North Polar expedition appear to prove that in the immediate vicinity of the magnetic pole the development of light is not in the least degree more intense or frequent than at some distance from it. MENSURATION. To find the solid contents of a cube : (1) Find the solid contents of a cube which is 5 ft. each way. (2) What is the solid contents of a marble cube which is 7 ft. 6 in. each way? (3) How many 3-in. cubes can be cut out of a cube of marble which is 3 ft. each way? (4) What is the weight of a leaden cube which is 15 in. each way, the specific gravity of lead being 115, and the weight of a cubic foot of water 1000 ounces avoirdupois? (5) What weight of water will a cubical cistern contain which is 4 ft. 5 in. each way? |