With this accords one of the visions with which the beloved disciple was favoured. Rev. iv. 3. Admitted into the immediate presence of God, he beheld a glorious throne, on which One sat, whom he did not attempt to describe. Here, then, was an emblem of the universal, absolute, and eternal dominion of Jehovah; and of his exaltation as the great Creator and Sovereign Lord of all creatures.

As throughout these visions there is an allusion to the Temple, its furniture and services, the visible glory may have had some reference to that above the mercyseat in the holy of holies; its being resplendent like the jasper, might be emblematical of the perfect purity and excellency of the Divine nature; and its colour like the red sardine stone, might represent his awful justice and fiery indignation. It is said, moreover, "there was a rainbow round about the throne, in sight like unto an emerald:" thus intimating that the holiness and justice of God, and all his dispensations as the Sovereign of the universe, had respect to his covenant of peace, with which they fully harmonized. It has been supposed that as in this rainbow the soft green of the emerald was predominant, it might perhaps imply, that as the green relieves the eye which is fatigued and dazzled by some others, so the discovery of God's

mercy in the covenant of grace soothes and refreshes the mind, which might otherwise be dismayed by the glories of his power, justice, and holiness.

Many peculiar rainbows have been seen and described. One occurred when a cloud charged with rain was passing, which produced a darkness so dense that the surface of the water on which the observer was sailing, was quite obscured at a little distance. When it first began to disperse, a bright luminous appearance, tinged with prismatic colours, was seen emerging from the obscurity. The voyager was near the European coast, and by degrees it formed a bright arch, the legs resting about 100 yards on each side of him, and the apex on the other shore. Unlike other rainbows, it was perfectly horizontal, and lay flat on the water, to which it communicated a very beautiful and extraordinary aspect. It exactly resembled a brilliant rainbow suddenly cast down from the sky, and laid prostrate on the surface of the sea. It continued to accompany the boat for about fifteen minutes, when the sky cleared, and the beautiful object melted into air.

It is, however, a very remarkable fact, that, apart from the sun's rays, there is no such thing in nature as colour. All bodies, so far as this is concerned, are therefore alike in the dark. A change in their appear

EXPERIMENTS OF NEWTON.

91

ance, however, may very easily be made. What seems more pure than the driven snow? yet if some of it be placed in a vessel by the fire-side, what becomes of its whiteness? A candle, however bright, placed under a cover, so that the smoke may be arrested in its ascent, leaves soot on the surface. Loaf-sugar melted over the fire, first turns brown, afterwards black, and a single grain of this colour will give a quart of pure water a yellow tinge.

The science of colour is full of wonders. Light is often considered as a simple substance, but this is far from being the case. The white light which comes from the sun, or any other luminous body, is generally considered as composed of seven different kinds of light, of different colours-red, blue, yellow, green, orange, indigo, and violet.

To the experiments of Sir Isaac Newton we are much indebted. A statue of him, as engaged in them, appears in Trinity College, Cambridge.

Having determined that a beam of white light, as emitted from the sun, consisted of seven colours, which possess different degrees of refrangibility, he measured the relative extent of the coloured spaces, and found them to have the proportions of the following figure. It presents a lengthened image of the sun, produced by

the rays being separated in different degrees from their original direction :—

Red

Orange

Yellow

Green

Blue

Indigo

Violet

If we were required to decompose a greenish gray powder, consisting of fine brass and fine steel filings, we should do it by putting into the powder a loadstone, which would instantly attract all the blue steel filings, and leave behind the yellow brass filings, thus reducing the greenish gray powder into the yellow and blue dust of which it is formed. If, too, all the steel filings were much smaller than those of brass, a sieve, whose meshes would permit the steel to pass, while the brass was retained, would have separated them still more quickly.

DECOMPOSITION OF LIGHT.

93

To separate the colours of a ray of light, different means must be employed.

A

R

An optical prism, shown at A, is a solid glass, having two plane surfaces, A R, A S, which are called its refracting surfaces. The face R S is called the base of the prism. Now light may be as easily and speedily decomposed, by means of such a triangular piece of glass. To use it, the window-shutters should be closed, and a ray of light admitted through a small hole; as this falls on the prism, all the colours of the rainbow will be cast on the opposite wall, as in the previous figure, and with a brightness rarely equalled. An effect in some respects similar, yet of course inferior, is produced when the rays of the sun fall on lustres of cut glass. The prism, however, did not form these colours; they existed in the ray before its refraction by the glass; and when combined, they recomposed white light. This may be proved, rudely, though accurately enough for the purpose, by mixing together the seven colours in the following proportions:-red 45;