marked. By the middle of the afternoon, the whole, for many miles, presented the usual summer dress. The instinct of plants is very remarkable, or the sensible indications afforded of their dependence upon the luminous element. The stately head of the annual sun-flower moves with the sun from east to west, returning by natural elasticity after sunset to the east, to meet the solar beams in the morning; the innumerable leaves of a clover-field follow the same course; and all plants, more or less, pay the same deference to sunlight. Those of the hothouse will direct their branches to the side where it is most copious, and not to the quarter of the heated flue, or where the most air is admitted.

Further analysis of the solar beam has unveiled an additional phenomenon, that of calorific or heat-exciting rays, distinct from the luminous. Equally as influential and benign is their agency in the realm of nature. The evidence of this is at once supplied by the contrast everywhere between summer and winter, and the different scenery of the equator and the poles. But besides contributing to the direct development of life in the animal and vegetable kingdoms, the calorific rays produce a variety of remarkable effects upon the inorganic creation, without which this could not be a habitable world. The sun warms the earth; the earth imparts its warmth to the overlying air; the warmed air expands, becomes lighter, and rises; and a current of colder air at once proceeds to take its place, to experience the same change. Thus the winds are put in motion to freshen the atmosphere, maintain its salubrity by preserving the due admixture of its components, and enable the mariner to sail across the deep. By the agency, also, of the solar heat, aqueous particles

are exhaled from the ocean, lakes, rivers, and moist earth, from which we have clouds,-reservoirs of water in the air,-finally discharging their contents upon the land in fertilizing showers of rain or snow. Such is the heating power of the solar rays, that some of the men employed in the construction of the Plymouth Breakwater had their caps burnt in a diving-bell thirty feet under the surface of the sea, from inadvertently sitting under the focal point of the convex glasses in the upper part of the machine.

Distinct from the luminous and heating principles in the sunbeam, there are the chemical rays, which excite neither light nor heat, but speedily produce peculiar changes in certain substances exposed to their action, as in the white chloride of silver, which is blackened in a few minutes on being placed in the sunshine. The apparently magical photographic processes by which true, delicate, and beautiful images are instantaneously produced, are founded upon the action of the chemical rays; and the diversities of complexion which distinguish the human race—the copper of the Indian, and the ebony of the negro, appear to be chiefly due to their influence. In fact, the entire surface of the earth, with all its plants and animals-the granite rock which meets with firmness the driving storm; the stones which form the "cloud-capt towers and gorgeous palaces" of the architect; the marble which the artist chisels into life-like memorials of departed greatness-are all acted upon, more or less, by the chemical and molecular disturbing power of the sunshine, and would all speedily perish if incessantly exposed to the delicate but potent touch of its beams. Hence darkness and rest, night and sleep, are needful for mountains and valleys, as well as for plants, animals, and man;

for science has determined, though it has not solved the mode, that, during those intervals, nature rectifies the chemical disturbances and molecular changes effected in the daytime. Therefore "the sun knoweth his going down. Thou makest darkness, and it is night. Man goeth forth unto his work and to his labour until the evening. O Lord, how manifold are thy works! in wisdom hast thou made them all: the earth is full of thy riches."

There remains to be noticed a singular and interesting, but mysterious appearance, accompanying the sun, long known under the name of the Zodiacal light, from its path lying obliquely in the zodiac. This is a glow, or beam of light, of a conical form, rounded at the vertex, and with the base at the horizon. Though usually faint and white, it is sometimes bright and rosy, yet generally so transparent that the feeblest stars may be seen as distinctly through it as in other parts of the sky. In our latitude, in clear weather, it may be observed after sunset in the spring months, and before sunrise at the opposite season; but it is never so definite to us as it appears in tropical countries. Kepler noticed the zodiacal light; and from some intimations in Pliny it may be inferred not to have been unknown to the ancients. But it attracted little attention till the elder Cassini regularly described it in 1683. The nature of this object is perfectly obscure. It has been considered to be the solar atmosphere, receiving its peculiar form, that of a long narrow ellipse, only the half of which we can ever see, from the rotation of the sun upon its axis. But Sir John Herschel conceives it may be the denser part of that medium, which, there is reason to believe, resists the motions of comets loaded perhaps with the tails of

millions of those bodies, of which they have been stripped in their approach to the central orb, and which may be slowly subsiding to it.

Such is the sun,

"Great source of day! best image here below

Of the Creator."

Moses referred to the "precious fruits" brought forth by it when pronouncing the blessing of the tribe of Joseph; and in every age, as the early dawn has chased away the shades of night, the rudest nations have hailed the rising sun as in some manner intimately connected with the welfare of every object enjoying animal and vegetable life. This connexion, together with the ineffable glory, originated in unenlightened times the idolatry of the solar orb. Inspired wisdom teaches us to admire the material splendour, and to note its benefits, but to magnify the Divine hand in the formation of the wondrous globe. "The day is thine, the night also is thine: thou hast prepared the light and the sun.” The position of the source of light and heat in the mechanism of nature is strikingly illustrative of intelligent and beneficial contrivance, for, obviously, the collection of the self-luminous matter in a vast mass at the centre of the solar system is the arrangement best adapted to secure the uniform, regular, and most liberal distribution of its influence through it. Hence, while we admire the all-pervading, bright, and life-sustaining sunbeam, and mark all nature rejoicing in its rays, while beautified to the eye by them, it is true philosophy, as well as true religion, to respond to the sentiment expressed in the psalmody of Israel :-"Oh give thanks unto the Lord;-to him that made great lights: the sun to rule the day: for his mercy endureth for ever."

F

CHAPTER IV.

MERCURY, VENUS, AND THEIR TRANSITS.

The Solar System- Inferior or Interior Planets-Sensible evidence of relative position-Mercury-Elements of the Planet-Difficulty of observation -First recorded Transit-Succeeding Transits-Lalande-Le Verrier and Mitchell Venus - Elements of the Planet - Phases - First observed Transit-Youthful Astronomers of Lancashire and Yorkshire-Horrocks -Particulars respecting him-Predicts the Transit of 1639-His Observation of it-His death-Memorials of Horrocks-Subsequent Transits-The Evening and Morning Star.

THAT portion of the universe of which the sun is the centre, as at present known, consists of eight principal planets revolving round it in the following order as to distance-Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; eighteen satellites attending these primary bodies, and circulating round them, of which the Earth has one, Jupiter four, Saturn eight, Uranus four, and Neptune one; 130 minor planets between the paths of Mars and Jupiter, also in revolution round the solar globe; and several comets, whose entire orbits are included within the planetary paths, besides hundreds of others which appear within the visible limits of the system, approach the sun, and retire from it into the depths of space. This makes a total of 156 planets and satellites, dependent upon, and controlled by, the attractive force of the central body. Of this number the ancients were only acquainted with six-the Moon, Mercury, Venus, Mars, Jupiter, and Saturn; and no more were known down to the commencement of the seventeenth century. Ten