wonderful character.

Instead of finding the sun everywhere

equally brilliant, the telescope shows sometimes on its surface black spots, of very irregular figure, jagged and broken in outline, and surrounded by a penumbra conforming in figure to the general outline of the central black spot (called the nucleus), but of much lighter shade. Even where there are no spots, the surface of the sun is by no means uniformly brilliant. The entire surface has a mottled appearance, with delicate pores or points, no one of which can be readily held by the eye, but a group of them may sometimes be seized by the vision under favourable atmospheric circumstances, and can be held long enough to demonstrate that these minute pores do not change their relative position, or disappear while under the eye.

Besides the mottling of the surface, the telescope detects in the solar orb a variety of brighter streaks, called faculæ, whose appearance has been connected, as some believe, with the breaking out of the black spots.

Watching from day to day a single spot, or a group of spots on the sun's surface, they are found to advance together in the same direction, slowly to approach the edge of the sun, finally to disappear from the sight, and after a certain number of days to re-appear on the opposite side of the sun's disc, revealing the surprising fact that the sun is slowly rotating on an axis whose position seems to be invariable. In case these spots were absolutely fixed on the sun's surface, they would reveal the exact period in which his rotation is performed; but in consequence of their change of figure, and change of position as well, we can only reach an approximate value of the period of rotation. This is now fixed, by the best authorities, at twenty-fiv days, eight hours and nine minutes.

During the past thirty years, M. Schwabe, of Dessau,* has given special daily attention to counting the groups and spots on the sun; and by preserving a record, it has been

* In Hanalt, Germany.

discovered that the amount of solar surface covered by the black spots is not only variable, but that periodicitg marks this variation. The entire change, from a maximum of spots counted in any year, to the minimum, occupies about five and a half years, and the same time elapses from a minimum to a maximum, making the period from maximum to maximum eleven years. This fact is one of the most surprising revealed in the physical constitution of any of the heavenly bodies, and thus far has baffled the power of human investigation to explain it, while its mysterious character is increased by the fact recently discovered, that this periodicity in the solar spots is identical in duration with a certain variation observed in the intensity of terrestrial magnetism. Thus, it would seem, that a new bond of union is about to be established between the earth we inhabit and that mighty orb whence we receive our supplies of light and heat.

Some astronomers account for the solar spots by supposing the sun to be a solid, dark, opaque globe, surrounded by two atmospheres, the exterior one a highly luminous and gaseous envelope, the interior more dense, and possessing great reflecting power. The spots are supposed to result from powerful internal convulsions, upheavals from within breaking through these two envelopes, and producing a more extended chasm in the external luminous atmosphere. I have examined the surface of the sun and closely observed the large solar spots with a refractor of admirable performance, and so far from presenting an appearance such as the above hypothesis would warrant, the entire exhibition resembled the openings often found by melting through a thick stratum of solid ice from below--the spiky and jagged outline of the black nucleus being well represented by a similar form in the opening through the ice, while the penumbra was very faithfully represented by the thinner portions of ice remaining around the opening. It is not to be inferred from this comparison that the author entertains the opinion that the exterior of the sun is a solid crust, and that these solar spots are produced from the melting of this

crust by the action of internal fires. The comparison is made for the purpose of illustrating, as strongly as possible, the absolute appearance of these inexplicable phenomena, and to present as strong a contrast as the facts warrant to the statement made by a distinguished astronomer, that the sun's surface, when viewed by a powerful telescope, resembles "the subsidence of some flocculent chemical precipitates in a transparent fluid.” So far from this being the case, the sharp outline of the penumbra surrounding the dark spots has often been seen to cut directly across the minute pores, dividing them sharply and sometimes equally.

Recent observations seem to demonstrate that what has generally been considered the solar surface is really the exterior of a cloudy atmosphere beneath the luminous ocean surrounding the sun. Mr. Dawes, by an eye-piece of his own construction, bearing a metallic diaphragm, in which a minute hole is pierced, coincident with the axis of the telescope, has been enabled to make a very critical examination of the solar spots. He finds in the centre of the dark spot a smaller opening, which is, as now seen, intensely black, and this is at present regarded as the real surface of the solar orb. The same distinguished observer has announced the discovery of an actual rotation of the solar spots about a central axis. This important fact has given rise to speculation as to the probable cause of these wonderful fluctuations which occur in the solar atmospheres.

It is conjectured that these exhibitions may be produced by tremendous storms or whirlwinds resembling those which sometimes sweep over the surface of the earth, and whose vortices, if seen from above, would present an appearance not unlike the spots on the sun. We understand how these tornadoes are generated in the atmosphere of the earth, but it is useless to attempt to conjecture the causes which can produce such amazing effects in the solar atmosphere.

INTENSITY OF THE SOLAR HEAT.-Admitting that the heat of the sun falling on the earth is diminished in the ratio of the square of the sun's distance, it is not diflicult to form