THE surpassing splendour of the Sun, as compared with that of any of the other orbs of the firmament, is not more impressive than his stupendous magnitude, and the important functions which it is his prerogative to fulfil. Situated at the centre of our system-of which he may be regarded as 'both eye and soul '-the orb has a diameter approaching 1,000,000 miles, and a mass 750 times greater than that of all the planets combined. These, by his attractive power, he retains in their several paths and orbits, and even far distant Neptune acknowledges his potent sway. With prodigal liberality he dispenses his vast stores of light and heat, which illumine and vivify the worlds circling around him, and upon the constant supply of which all animated beings depend for their existence. Deprived of the light of the Sun, this world would be enveloped in perpetual darkness, and we should all miserably perish.

The Sun is distant from the Earth about 93,000,000 miles. His diameter is 867,000 miles,

or nearly four times the extent of the radius of the Moon's orbit. The mass of the orb exceeds that of the Earth 330,000 times, and in volume 1,305,000 times. The Sun is a sphere, and rotates on his axis from west to east in 25 days 8 hours. The velocity of a point at the solar equator is 4,407 miles an hour. The density of the Sun is only one-fourth that of the Earth, or, in other words, bulk for bulk, the Earth is four times heavier than the Sun. The force of gravity at the Sun's surface is twenty-seven times greater than it is on the Earth; it would therefore be impossible for beings constituted as we are to exist on the solar surface.

The dazzling luminous envelope which indicates to the naked eye the boundary of the solar disc is called the РHOTOSPHERE. It is most brilliant at the centre of the Sun, and diminishes in brightness towards the circumference, where its luminosity is but one-fourth that of the central portion of the disc. The photosphere consists of gaseous vapours or clouds, of irregular form and size, separated by less brilliant interstices, and glowing white with the heat derived from the interior of the Sun. In the telescope the photosphere is not of uniform brilliancy, but presents a mottled or granular appearance, an effect created by the intermixture of spaces of unequal brightness. Small nodules of intense brilliance, resembling 'rice-grains,' but which, according to Nasmyth, are of a willow-leaf shape with pointed extremities, which form a network over portions of the photosphere, are sprinkled profusely over a more

faintly luminous background. These 'grains' consist of irregular rounded masses, having an area of several hundred miles. By the application of a high magnifying power they can be resolved into 'granules '-minute luminous dots which constitute onefifth of the Sun's surface and emit three-fourths of the light. This granulation is not uniform over the surface of the photosphere; in some parts it is indistinct, and appears to be replaced by interlacing filamentous bands, which are most apparent in the penumbræ of the spots and around the spots themselves. The 'granules' are the tops of ascending masses of intensely luminous vapour; the comparatively dark 'pores' consist of similar descending masses, which, having radiated their energy, are returning to be again heated underneath the surface of the photosphere.

In certain regions of the photosphere several dark patches are usually visible, which are called 'sun-spots.' At occasional times they are almost entirely absent from the solar disc. It has been observed that they occupy a zone extending from 10° to 35° north and south of the solar equator, but are not found in the equatorial and polar regions of the Sun. A sun-spot is usually described as consisting of an irregular dark central portion, called the umbra; surrounding it is an edging or fringe less dark, consisting of filaments radiating inwards called the penumbra. Within the umbra there is sometimes seen a still darker spot, called the nucleus. The umbra is generally uniformly dark, but at times

filmy luminous clouds have been observed floating over it. The nucleus is believed to be the orifice of a tubular depression in the floor of the umbra, prolonged downwards to an unknown depth. The penumbra is brightest at its inner edge, where the filaments present a marked contrast when compared

with the dark cavity of the umbra which they surround and overhang. Sometimes lengthened processes unite with those of the opposite side and form bands and bridges' across the umbra. The darkest portion of the penumbra is its external edge, which stands out conspicuously against the adjoin

ing bright surface of the Sun. One penumbra will sometimes enclose several umbræ whilst the nuclei may be entirely wanting.

Sun-spots usually appear in groups; large isolated spots are of rare occurrence, and are generally accompanied by several smaller ones of less perfect formation. The exact moment of the origin of a sun-spot cannot be ascertained, because it arises from an imperceptible point; it grows very rapidly, and often attains its full size in a day.

When

Prior to its appearance there is an unusual disturbance of the solar surface over the site of the spot: luminous ridges, called faculæ, and dark pores' become conspicuous, between which greyish patches appear, that seem to lie underneath a thin layer of the photosphere; this is rapidly dispelled and a fully formed spot comes into view. a sun-spot has completed its period of existence, the photospheric matter overwhelms the penumbra, and rushes into the umbra, which it obliterates, causing the spot to disappear. The duration of sun-spots is subject to considerable variation; some last for weeks or months, and others for a few days or hours. A spot when once fully formed maintains its shape, which is usually rounded, until the period of its breaking up. Spots of long duration rotate with the Sun. Those which become visible at the edge of the Sun's limb have been observed to travel across his disc in less than a fortnight, disappearing at the margin of the opposite limb; afterwards, if sufficiently long-lived, they have reappeared in