Look at a cloudy speck in Orion, visible, without aid, to the well-trained eye; that is a stellar universe of majesty altogether transcendent, lying at the verge of what is known. And if any of these lights from afar, on which the six-feet mirror is now casting its longing eye, resemble in character that spot, the systems from which they come are situated so deep in space that no ray from them could reach our earth until after travelling through the intervening abysses, during centuries whose number stuns the imagination. There must be some regarding which that faint illumination informs us, not of their present existence, but only that assuredly they were, and sent forth into the infinite the rays at present reaching us, at an epoch further back into the past than this momentary lifetime of man, by at least thirty millions of years!"

Sir David Brewster remarks: "In looking back upon what the Telescope has accomplished; in reckoning the thousands of celestial bodies which have been detected and surveyed; in reflecting on the vast depths of ether which have been sounded, and on the extensive fields of sidereal matter out of which worlds and systems of worlds are forming, and to be formed-can we doubt it to be the Divine plan that man shall yet discover the whole scheme of the visible universe, and that it is his individual duty, as well as the high prerogative of his order, to expound its mysteries and develop its laws. Over the invisible world he has received no commission to reign, and into its secrets he has no authority to look. It is over the material and the visible that he has to sway the intellectual sceptre; it is among the structures of organic and inorganic life that his functions of combination and analysis are to be chiefly exercised. Nor is his task unworthy of his genius, or unconnected with his destiny. Placed upon a globe already formed, and constituting part of a system already complete, he can scarcely trace, either in the solid masses around him, or in the forms and movements of the planets, any of those secondary causes by which these bodies have been shaped and launched on their journey. But in the distant heavens, where creation seemed to be ever active, where vast distance gives us the vision of huge magnitude, and where extended operations are actually going on, we may study the cosmogony of our system, and mark, even during the brief space of human life, the formation of a planet in the consolidation of the nebulous system which surrounds it."

THE MICROSCOPE.

O remarkable is the position of the Telescope and the Microscope, among the great inventions of the age, that no other instrument, and no other process but that which they embody, could make the slightest approximation to the secrets which they disclose. And, without the Telescope and the Microscope, the human eye would have struggle din vain to study the worlds beyond our own, and the elaborate structures of the organic and inorganic creation could never have been revealed.

How wondrous is the power of the eye! The immense expanse of sky and ocean-the crowds and buildings of a city-the woods and hills and streams of a landscape-are all seen by it with the same distinctness with which it marks the forms and hues and dimensions of the minute flower or insect. It is the most valuable of our organs of sense, and our admiration of the wondrous adaptations of the universe we inhabit is increased by the fact that light is provided for this organ. Through the aid of light the figure of any object is pictured on the retina of the eye, just in proportion to its distance. It is upon what philosophers call the "incidence of light" that our vision thus depends.

From the extremities of every object rays are carried to the centre of the human pupil, or sight-portion of the eyeball. Now, lines drawn from the extremities of an object to the eye must describe a triangle, of which the object forms one side. The more distant the object, the longer must the sides of the triangle be, and the smaller the object will appear; nearer it is, the shorter will be the sides, the greater will be the angle, and the larger will be the apparent size of the object observed.

It is on this principle that both Microscopes and Telescopes are formed. By the invention of a lens, or a convex glass, it is perceived that the rays of light passed through it are made to converge, through the concentrative power of the glass, very rapidly to a given point. If these rays converge to the inside, they of course diverge towards the outside. If a lens, or spherical piece of glass, therefore, be placed between the eye and any object within a short distance, the natural result will be that large and angular rays will be formed between it and the eye of the observer, and thus all its parts will be greatly magnified in appearance.

Or, in other words, the crystalline lens of the eye diminishes in density from the centre to the circumference: it is composed of successive concentric laminæ, each consisting of minute transparent fibres, varying in thickness, and arranged with the most beautiful symmetry in relation to the axis of vision. In some of the lower animals, the structure of the crystalline lens is more perfectly displayed than in man, and exhibits most striking phenomena both in reference to the variations of its density and the distribution of its fibres. The complication of its parts in some animals, and the admirable skill with which they are suited to the various purposes of their existence, exceed all description, and confound all human intelligence. Hence, very good Microscopes have been made with the crystalline lens of fish, birds, and quadrupeds.

Previous to the invention of glass, the Telescope and Microscope of the present day could not have been constructed, even had their theory been known; but it seems strange that a variety of facts which must have presented themselves to the most careless observer should not have led to the earlier construction of the Microscope. Through the spherical drops of water suspended before his eye, an attentive observer might have seen magnified some minute body placed accidentally in its anterior focus; and in the eyes of fishes and quadrupeds which he used for his food he might have seen, and might have extracted, the beautiful lenses which they contain. Curiosity might have prompted him to look through these remarkable lenses or spheres; and had he placed the lens of the smallest minnow, or that of a bird or sheep, or the ox, in or before a circular aperture, he would have possessed a Microscope of excellent quality, and different magnifying

powers. No such observations, however, seem to have been made, and even after the invention of glass, and its conversion into globular vessels, through which, when filled with any fluid, objects are magnified, the instrument remained undiscovered; though a small globe of glass, or of any transparent substance, makes a Microscope.

The earliest magnifying lens is that rudely made of rock crystal, which Mr. Layard found among a number of glass bowls in the north-west palace of Nimroud. It has been carefully examined by Sir David Brewster, who assigns reasons why this must be looked upon as a true optical lens. In reference to this, two remarkable facts in Layard's latest work on Nineveh show that the national records were written on bricks, in characters so small as scarcely to be legible without a Microscope, such as the above, found among the ruins of Nimroud early in the first century. Seneca incidentally alludes to the magnifying powers of a glass globe filled with water; and this may have led the observer to try the effect of smaller globes, and thus obtain magnifying powers sufficient to discover phenomena otherwise invisible. Lenses of glass were undoubtedly in existence in the time of Pliny; but at that period, and for many centuries afterwards, they appear to have been used only as burning, or reading glasses; and not to have been made so small as to be used for a single Microscope.

In the Microscope, the next object to be obtained in its construction, after its magnifying power, is the clearness with which it can be perceived. The principle is much the same as in the Telescope; and the chief difference observable in the two instruments appears to be, that in the Microscope the main object is to obtain intensity at a short distance, and in the Telescope the cumulation of power through a focal length: that is, to make the distance between the eye of the observer and the place where the rays would diverge to either side of the object, as long as possible. For the longer the focal length, the greater will be the cumulative and penetrative power of the glass; and the introduction of several glasses, as is the case in the best instruments, is only made for the purpose of strengthening the effect.

The following is the method of determining the magnifying power of glasses employed in the single Microscope. If the focus of a convex lens be at one end, and the natural sight at

eight inches, which is the common standard, an object may be seen through that line at one inch distant from the eye, and will appear in its diameter eight times larger than to the naked eye. But as the object is magnified every way equally, in length as well as in breadth, we must square this diameter, to know how much it in reality appears enlarged; and we shall then find its superficies is magnified 64 times.

The so-called magnifying power of a lens applied to the eye, as in a Microscope, is derived from its enabling the eye to approach more nearly to its object than would otherwise be compatible with distinct vision. A striking proof of this statement may be obtained by the following simple and instructive experiment: Take any minute object, a very small insect, for instance, held on a pin, or gummed to a slip of glass; then present it to a strong light, and look at it through the finest needle-hole in a blackened card placed about an inch before it. The insect will appear quite distinct, and about ten times larger than its usual size. Then suddenly withdraw the card without disturbing the object, which will suddenly become indistinct, and nearly invisible. The reason is that the naked eye cannot see at so small a distance as one inch. But the card with the hole having enabled the eye to approach within an inch, and to see distinctly at that distance, is thus proved to be as decidedly a magnifying instrument as any lens, or combination of lenses.

As in all great inventions, we can hardly venture to ascribe that of the Microscope to any single individual. Nor has any person claimed to be the inventor of the single Microscope. Huygens is of opinion that this instrument was invented not long after the Telescope, and ten years earlier than the compound Microscope; he tells us that in 1621, Microscopes of this kind were seen in possession of Cornelius Debrell of Alkinaar, who resided in London, as Mathematician to James VI.; and, adds Huygens, "those who were present have often told me this, and also that he was the first inventor of them." This statement is, however, contrary to that of Peter Borell, Dutch Ambassador in 1691, who says that Debrell showed him a Microscope, which had been made by Jansen, the spectacle-maker at Middleburg, in 1590, and presented to the Archduke of Austria; it was said to be six feet long. In the Preface to the Works of Galileo, published at Milan in 1808, it is stated that Galileo invented the Micro