There is one property of light, called refraction, which I will mention here, because it is capable of a very easy and familiar illustration, and will account. for a very common, but seemingly extraordinary phenomenon. When a ray of light passes out of one medium into another, it is refracted, or turned out of its first course, according as it falls more or less obliquely on the refracting surface which divides the two mediums. Any person may exemplify this by the following experiment: put a shilling in an empty basin, and retire to such a distance, that the edge of the basin shall just hide it from your sight; then keeping yourself steady, let another person fill the vessel gently with water; and, as the water rises toward the top, the shilling will become more and more visible, till, at length, the whole of it will be distinctly seen, appearing as if it had been raised above the bottom of the basin.

This proves, that the rays of light are refracted, or bent downward, in their passage out of the water into the air; and as they now come to the eye in a more oblique direction, the object must necessarily appear to be elevated, and in a different situation. from that in which it was really placed. The same thing may also be shown thus: place the basin in such a manner, that the sun may shine obliquely on it, and observe where the shadow of the rim falls upon the bottom; then fill it with water, and the shadow will not extend so far as it did when the vessel was empty; which shows that the rays have changed their direction, by passing out of one me dium into another of a different density.

The less obliquely the rays fall, the less they will be refracted; and if they fall perpendicularly, they will not be refracted at all. For, in the last experiment, the higher the sun rises, the less will be the difference between the places, where the edge of the shadow falls, in the empty and full basin. And

if a stick be laid across the basin, and the sun's rays be reflected perpendicularly into it from a lookingglass, the shadow of the stick will fall upon the same part of the bottom, whether the basin be full or empty. The same effects will also take place, when the experiment is performed with any other fluid: but the denser the medium, the more will light be refracted in passing through it.

From these observations it will readily appear, that objects can seldom be seen in their true places. We are deceived by every thing around us: the sight is no less subject to error than the rest of our senses; though they all contribute to our pleasure, and promote our happiness by various means. In consequence of this property of refraction, we enjoy the sight of the sun when he is really below the horizon, for a little time before his rising and for a little time after his setting. This is also the cause which produces the crepusculum, or morning and evening twilight: for the rays of the sun, in falling upon the higher part of the atmosphere, are reflected back to our eyes, and form a faint light, which gradually augments till it becomes day. It is in those brilliant colours which paint the clouds, before the rising of the sun, that the poets have placed Aurora, or the goddess of the morn: she opens the gates of day with her rosy fingers; and the daughter of the Air and of the Sun has her throne in the atmosphere.

Had no such atmosphere existed, the rays of light would have come to us in straight lines, and the appearance and disappearance of the sun would have been instantaneous; we should have had a sudden transition from the brightest sunshine to the most profound darkness, and from thick darkness to a blaze of light. Refraction, therefore, is extremely useful, not only as it prepares us gradually for the light of the sun, but as it occasions twilight, and

thus prolongs the duration of the day. Nature has established these gradations, to heighten our pleasures by variety; the scene is perpetually changing, but the order of things is immutable.

With what exalted sentiments of devotion ought the Contemplative Philosopher to consider the various and unspeakably beautiful phenomena of light! We find it to be little less than the life and pleasure of all animated beings. Of what benefit, indeed, could life be; what pleasure, what comfort could we enjoy, in the horrors of perpetual darkness? How could we provide ourselves with food, and the other necessaries of life? How could we transact the least business? How could we correspond with each other, or be of the least reciprocal service, without light, and those admirable organs of the body, which the Omnipotent Creator has adapted to the perception of this inestimable benefit?

But it is unnecessary to enumerate the inexpressible advantages of a blessing, of which the most inattentive of mankind must be sensible. What is applied to Wisdom, in the book called The Wisdom of Solomon, She is a pure influence flowing from the glory of the Almighty-she is the brightness of the everlasting Light, has been applied by Milton to Light, with the most beautiful propriety :

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Bright effluence of bright essence increate.

In a word, when we consider the wonderful beauty and pleasures of which light is the essential source, with how much is still involved in mystery, notwithstanding the most diligent inquiries into its nature and properties, by the most illustrious phi losophers, well may we exclaim in the beautiful language of Thomson:

How then shall I attempt to sing of Him
Who, Light Himself, in uncreated light

Invested deep, dwells awfully retired
From mortal eye, or angel's purer ken;
Whose single smile has, from the first of time,
Filled, overflowing, all yon lamps of heaven,
That beam for ever through the boundless sky:
But, should He hide his face, th' astonished sun,
And all th' extinguished stars, would loosening reel
Wide from their spheres, and Chaos come again,

No. XLV.

ON COLOURS.

Colours are but the phantoms of the day,
With that they're born, with that they fade away;
Like beauty's charms, they but amuse the sight,
Dark in themselves, till by reflection bright;
With the sun's aid to rival him they boast,

But light withdrawn, in their own shades are lost.

HUGHES.

THE inquiry, in my former paper, into the nature and properties of light, leads me to consider next the admirable relations which the Deity has established between light itself and the surfaces of different bodies, whence proceed the various pheno-, mena of colours.

Different are the opinions of ancient and modern authors, and of the several sects of philosophers, with regard to the nature and origin of the phenomenon colour. The most popular opinion was long that of Aristotle, who maintained colour to be a property residing in the coloured body, and to exist independently of light. But to this doctrine it was

objected, that the neck and feathers of a pigeon or a peacock change their colours, according to their positions. Thus Lucretius:

Pluma columbarum quo pacio in sole videtur, &c.

LIB. 11. 800-806.

The plumes that go around the pigeon's head
Sometimes look brisker with a deeper red;
And then, in different positions seen,
Show a gay sky, all intermixed with green:
And so in peacock's tails, all filled with light,
The colour varies with the change of site.

CREECH.

It is now universally admitted, that colour is a property inherent in fight, whereby, according to the different sizes and magnitudes of its parts, it excites different vibrations in the fibres of the optic nerve; which, propagated to the sensorium, affect the mind with different sensations. Or colour may be defined a sensation of the soul, excited by the application of light to the retina of the eye; and different, as that light differs in the degree of its refrangibility, and the magnitude of its component parts.

The philosophy of colours is not unnoticed by the poets: Cowley, in particular, thus addresses Light, in a beautiful hymn:

All the world's bravery, that delights our eyes,

Is but thy several liveries :

Thou the rich die on them bestow'st,

Thy nimble pencil paint'st the landscape as thou go'st.

A crimson garment in the rose thou wear'st;

A crown of studded gold thou bear'st;

The virgin lilies, in their white,

Are clad but with the lawn of almost naked light.

The violet, Spring's little infant, stands

Girt in thy purple swaddling-bands:

On the fair tulip thou dost doat;

Thou cloth'st it in a gay and party-coloured coat. i