reflection and refraction; the penny reflecting sunlight, and the reflected sunlight being refracted on its road to you.

When we look on the sun, at the moment of his setting, we see his body after it has actually passed below our horizon. The rays of sunlight, as they journey from the ether of space into our denser atmosphere, or from a less to a more dense layer of air, are bent or refracted out of their course, so that they reach our eyes over the rising surface of earth, which otherwise would hide the sun from sight.

It is well to understand that whatever we see, we see by virtue of its own brightness of the light which it gives forth. That light may be either intrinsic or reflected. A sun, a star, a lamp, a candle, shine by their own radiance. A planet, a world, a mirror, and all conceivable bodies or surfaces which have no light of their own, shine by borrowed brightness. Rays of light proceeding from a shining body fall upon a dark body, and rebounding thence enter your eyes, rendering the object visible to you.

If you wish to see a pond, a house, or a tree, it is not in the least necessary that the sun itself should shine upon your face ; such shining, in fact, would only hinder sight. It is only needful that the sun should shine on pond, or house, or tree, and that reflected sun-rays, rebounding thence, should carry its outlines to your eyes. If you wish to read a book at night, it is quite needless for the lamp to cast its glare upon you. The lamprays must fall upon the book; and those rays, rebounding, have to reach your eyes. The less you see of the lamp itself, the better.

Even so, the sun shines upon the moon's dark body and lights it up. And we see the moon best when the sun is not visible. When he is, the glare of sunlight commonly prevents our seeing the moon at all.

Thus, upon whatever object light-rays fall, from any bright body, that object is made visible by means of the light which it gives forth again. Some substances reflect much more light than others, and consequently they become more distinct, even more brilliant. But if a body gave forth no light whatever, our eyes could not detect its presence.

A looking-glass in full sunlight will flash radiant beams, while a heap of earth in a dark cellar can barely be seen at all. Yet both are visible from the same cause; only in the one case we have abundance of light and a good reflecting surface; in VOL. 85 (V.-NEW SERIES). NO. 507.

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the other case we have very little light thrown back from the surface.

When we talk of a ray of light journeying, or being reflected, we are using a convenient term to help our understandings; but in strict truth light no more comes in separate rays than a river flows in separate drops. The ideal drop of water is infinitesimally small; and the ideal ray of light is infinitesimally slender. The smallest surface which shines at all may be said to send millions of light-rays to the eye, to make its presence and appearance known. By magnifying that object, the so-called 'rays' can be multiplied and divided to almost any extent.

As light journeys through space it is invisible. It becomes visible only when arrested by some object in its path. Many people fail to grasp this fact, and picture the vast reaches of space as everywhere lighted up by countless brilliant suns, like an enormous room lighted by countless lamps and candles. Such a notion is wrong. Not only is the hugest room ever built a mere speck compared with heavenly space; but also in that room is something which does not exist in space.

the atmosphere.

I mean,

Air carries and spreads about light. Each particle of air to some extent arrests and reflects sunlight. In the wide reaches of space we do, indeed, believe that something exists, which has been named 'ether,' something exceedingly attenuated, something not to be compared with air in density, something without which light probably could not travel at all. But although ether may be a means of light passing from one object to another, it cannot stop the rays of light, as even one particle of air can do, causing them to give forth their brightness.

Through every part of space countless billions of light-rays are ever darting on interminable journeys from multitudinous suns; yet the vast gaps between those suns are dark, lighted only here and there probably by some world or comet or meteorite, which intercepts the hidden rays, and makes them visible.

Our sun gives out an enormous amount of heat and brightness. With only his present expenditure of both, he could light and warm and keep in life no less than two thousand two hundred millions of little worlds such as ours.

If all the planets of the Solar System, all the moons, all the comets, all the meteors and meteorites, were brought together, and the whole supply of solar heat and light received by them were subtracted, it would be found to be the merest fraction compared

with the sum total that is lavishly poured away into space. Poured away recklessly, poured away uselessly, so we might feel disposed to say; but what do we know about the matter?

That which to our limited understanding seems like waste, need not be waste. That which to us seems purposeless, may have some mighty cause underlying. If nothing else can be learnt from this abounding outflow of heat and light, so much at least is apparent, the Royal richness and fulness of DIVINE giving. Man may dole out his little gifts, just enough at a time for the moment's need. God gives grandly to His Universe, enough and to spare!

Still, it would be the height of rashness to assert that for all this wealth of sunlight and sun-heat, no use does, or can exist. We simply know nothing whatever about the matter!

An eye is that organ, by means of which a man perceives, or becomes conscious of, objects near or far, of which he would not know by means of his other senses.

True, those other senses can often be exercised in addition. When he sees a thing, he may also feel it, taste it, smell it, hear it, any or all. But by sight alone he can learn that an object exists, which he is unable to hear or smell, to taste or feel. He can discover something of its size and colour, its shape and position, through sight alone.

Remember, however, that the eye is only an organ. The eye itself does not see. It is merely the 'camera or optical instrument,' by means of which a man's brain is made aware of things outside himself; things often too distant for him to be conscious of them in any other mode. Moreover, that which your brain sees is not the object itself, but only a reflection of that object, thrown upon the retina of your eye,-more strictly still, only a message or idea of that image, telegraphed from the eye to the brain.

You say that you see the moon. Yet the moon is not touched by your eye. When you feel a table, the sensitive nerves of your finger-tips are in actual contact with the table. When you taste sugar, the sugar is within you, in actual contact with your nerves of taste. When you smell a rose, particles of the sweet essence of the rose have floated into your nose, coming into actual contact with the olfactory nerve. In all these cases, though the brain receives a message, it is a message direct from

the source, caused by positive touch between your nerves of sensation and the thing which is felt, tasted, or smelt.

But with hearing and with seeing actual contact ceases. You may hear an explosion miles away. You may see a sun millions or billions of miles away.

Yet something analogous to the sense of touch still comes in. When you hear a gun fired, half a mile off, the gun is not touched by your ear; nevertheless, something is sent from the exploding powder to the nerves within your ears, by means of which a message of noise reaches the brain. When you see a moon, tens of thousands of miles away, that moon is not touched by your eye; nevertheless, something is despatched from the moon to the nerves of your eyes, by means of which a message of light reaches the brain.

What is this something which travels to ear and to eye, like a telegraphic message?

Take the ear first. Sound journeys to the ear in waves of air. Any manner of concussion, however slight, produces such waves. One may even say that any manner of touch, however delicate, produces waves of sound. Our ears are so formed as to hear only certain degrees of air-vibrations; but, doubtless, innumerable vibrations take place which we are unable to hear, because they are too high, or too low, or too gentle, to affect our organs of hearing. A fly cannot walk across the window-pane without noise, though to us his footsteps are inaudible. A spider cannot crunch his victim without noise, though the crunching is unheard by us. A grain of sand cannot drop to the ground without noise, though finer ears than ours are required to detect the tiny jar. When a rock falls, or a lion munches, or a horse walks, our coarser sense of hearing is at once aware of the air-waves set in motion.

It must not be supposed that a wave of air is at all the same as wind. Wind is air in actual motion, travelling from one place to another; whereas, in a wave, the air-particles move very slightly, and do not travel at all.

A wave of water, out at sea, does not mean an onward motion of the water. Close to shore waves break and rush a little way up the beach; but away from land, where the real nature of a wave is apparent, it simply rises and falls. The wave itself travels onward; the water does not. The wave passes through the water, not carrying the water along. It is a vibration or impulse, communicated from particle to particle of water.

the wave passes, each water-particle makes a little motion, and returns to its former position. A piece of floating seaweed is not borne onward by the wave. It has a passing lift, and is left where it was.

Just so with waves of sound. Each wave is a vibration or impulse, which passes from particle to particle of air, giving it a stir, but not sweeping it onward. When rock is blasted at a distance, and the crash of explosion reaches your ears, you must not suppose for a moment that the air which was close to the blasted rock has come rushing to you. That would, indeed, be a hurricane ! All that the explosion has done is to set in motion waves of air,-undulations passing swiftly, far more swiftly than the most rapid hurricane, from particle to particle of air, and at length reaching the particles situated within your ears. By means of those undulations, news of the distant explosion is conveyed through your ear-drums to your brain ; and after long practice your brain has learnt to ascribe the airwaves in question to their true source.

We believe that light also is conveyed by waves, or by something analogous to waves; not waves of air, for our atmósphere is far too coarse a medium, but waves of luminiferous ether.

The Ether of Space has neither been seen nor felt, nor can its existence be absolutely proved; but that some such medium does exist no reasonable doubts can be felt. Light appears to be conveyed by exceedingly small and rapid waves of ether; waves set in motion by the clash of minute particles in any blazing or heated body: much as sound-waves are set in motion by the clash or friction of larger substances.

Sound-waves travel at the rate of 1140 feet each second; and many distinct waves or vibrations enter the ear during one second of time, from the source which causes the noise. Musical waves, adapted to our power of hearing, vary from about sixteen per second, to forty thousand per second. That is to say-the lowest bass-note, which we can detect, means 16 waves striking upon the ear-drum in the course of each second; while the highest treble-note means 40,000 waves striking upon the ear-drum in the course of each second. Waves of sound, coming to our ears in the shape of ten to twelve waves per second, or in the shape of fifty or sixty thousand waves per second, are absolutely unheard by us. Yet any amount of such waves may be travelling through the air at all times.