The marine barometer differs from that used on shore, in having its tube contracted in one place to a very narrow bore, so as to prevent that sudden rising and falling of the mercury, which every motion of the ship would else occasion.

Civilized Europe is now familiar with the barometer and its uses, and therefore, that Europeans may conceive the first feelings connected with it, they almost require to witness the astonishment or incredulity with which people of other parts still regard it. A Chinese once

conversing on the subject with the author, could only imagine of the barometer, that it was a gift of miraculous nature, which the God of Christians gave them in pity, to direct them in the long and perilous voyages which they undertook to unknown seas.

A barometer is of great use to persons employed about those mines in which hydrogen gas, or fire-damp, is generated and exists in the crevices. When the atmosphere becomes unusually light, the hydrogen being relieved from a part of the pressure which ordinarily confines it to its holes and lurking places, expands or issues forth to where it may meet the lamp of the miner, and explode to his destruction. In heavy states of the atmosphere, on the contrary, it is pressed back to its hiding places, and the miner advances with safety.

We see from this that any reservoir or vessel containing air would itself answer as a barometer, if the only opening to it were through a long tubular neck, containing a close sliding plug, for then, according to the weight and pressure of the external air, the density of that in the cavity would vary, and all changes would be marked by the position of the moveable plug. A beautiful barometer has really been made on this principle, by using a vessel of glass, with a long slender neck, in which a globule of mercury is the moveable plug.-Arnott.

LIGHT.

THE phenomena of light and vision have always been held to constitute a most interesting branch of natural science; whether in regard to the beauty of light, or its

utility. The beauty is seen spread over a varied landscape-among the beds of the flower-gardens, on the spangled meads, in the plumage of birds, in the clouds around the rising and setting sun, in the circles of the rainbow. And the utility may be judged of by the reflection, that had man been compelled to supply his wants by groping in utter and unchangeable darkness, even if originally created with all the knowledge now existing in the world, he could scarcely have secured his existence for one day. Indeed, the earth without light would have been an unfit abode even for grubs, generated and living always amidst their food. Eternal night would have been universal death. Light, then, while the beauteous garb of nature, clothing the garden and the meadowglowing in the ruby, sparkling in the diamond-is also the absolutely necessary medium of communication between living creatures and the universe around them. The rising sun is what converts the wilderness of darkness which night covered, and which to the young mind, not yet aware of the regularity of nature's changes, is so full of horror, into a visible and lovely paradise. No wonder, then, if in early ages of the world, man has often been seen bending the knee before the glorious luminary, and worshipping it as the God of Nature. When a

mariner, who has been toiling in midnight gloom and tempest, at last perceives the dawn of day, or even the rising of the moon, the waves seem to him less lofty, the wind is only half as fierce, sweet hope beams on him with the light of heaven, and brings gladness to his heart. A man, wherever placed in light, receives by the eye from every object around-from hill and tree, and even a single leaf-nay, from every point in every object, and at every moment of time, a messenger of light to tell him what is there, and in what condition. Were he omnipresent, or had he the power of flitting from place to place with the speed of the wind, he could scarcely be more promptly informed. And even in many cases where distance intervenes not, light can impart at once knowledge which, by any other conceivable means, could come only tediously, or not at all. For example, when the illuminated countenance is revealing the secret workings of the heart, the tongue would in vain try to speak, even in long phrases, what one smile of friendship or affection can in an instant

convey;—and had there been no light, man never could have been aware of the miniature worlds of life and activity which, even in a drop of water, the microscope discovers to him; nor could he have formed any idea of the admirable structure belonging to many minute objects. It is light, again, which gives the telegraph, by which men converse from hill to hill, or across an extent of raging sea-and which, pouring upon the eye through the optic tube, brings intelligence of events passing in the remotest regions of space.-Dr. Arnott.

THE MICROSCOPE.

THOUGH all the contrivances by which our perceptions of light, and of those things and properties of things which light reveals, are highly interesting, yet there is a peculiar interest about the microscope which does not belong to any of the others. Spectacles are of great use to those whose eyes are imperfect in their construction, or impaired by age; and the telescope not only extends our view as far as a straight line can reach on the surface of the earth, but it reveals the wonders of the heavens. It shows us the surface of the moon, rugged, dreary, and dry, and as different from that of our earth as we can well imagine one body to be from another; and when we point it on a clear night to the blue dome of the sky, the stars are multiplied beyond what our arithmetic can sum up, or even our imagination picture. We see that the creation is, to our comprehension, infinitely great; and what then must be our thoughts of Him Who called the whole into being without aid and without labour! "He spake, and it was done.”

But the microscope doubles the enjoyment to us; and actually reveals to our knowledge another creation, as wonderfully small as that, upon which we look with the telescope, is wonderfully great. It is, indeed, more wonderful, because more out of the line of our ordinary observation and experience. All that the telescope discloses, to us, is disclosed, as it were, to our ordinary vision; and in the most glorious sight that it gives us, we have always the feeling that it is distance only which is overcome, and that, if we could perform the journey, we should get the

same sight of the objects with our naked eyes without the aid of the glass.

When, however, we resort to the microscope, the glory which we behold is of quite another kind. The little dot of mould upon a decaying stem, or a withering leaf, which to our unaided sight is merely a stain of colour distinguishable from the rest of the surface and nothing more, becomes a forest of trees, as perfect in their structures as those which clothe the slopes of our mountains, and give to the landscape so much both of its beauty and its fertility.

And when we compare the size of the seeds of our trees with that of the trees themselves, and find that the germ which, when fully developed, becomes the keel or the mainmast of the most stately vessel, is not half the size of a common pea, how inconceivably minute must we suppose the germs of the individual trees in the forest of mould to be! When we find that their full-grown stature is merely colour to the eye, we cease to wonder why they should, according to their kinds, be found in all imaginable situations, and ready to develope themselves whenever those circumstances occur which are favourable for that purpose.

Nor is the minuteness and multitude of animated beings revealed by the microscope less wonderful. When viewed through that instrument, a drop of putrid water, or vinegar, or of water just tinged with the admixture of the sour paste of flour, is found to contain as many living inhabitants as a parish, or a county. Their formation, too, is as perfect, and their organization as nicely adapted to their element, as in the ordinary creatures which we admire the most, so that downward as far as the microscope can go, and we know not how much further-for we cannot imagine a limit-the display of Almighty power is as wonderful in the small as in the great.

And even in the most minute of those microscopic tribes, whether vegetable or animal, we find that they are as true to the law of their being as creatures of a larger growth. The mould which grows in the cells of a decaying apple, or the animalcule that is found in stale vinegar, never comes but in that substance; and never but when the substance is in the state fitted for its ap