the higher regions, contrary to the direct tendency of the rising sun to dissipate them, they accordingly reflect the red rays of light abundantly, and are considered as announcing a speedy precipitation of rain.”

"In the morning, in fine weather, the strata of the air near the surface of the earth alone, and in the lowest and most sheltered spots, are in a state of absolute dampness, the more elevated regions are comparatively free from humidity, and the morning light is grey; the vapours which, during the reversion of the process, might probably reflect the red rays, are not elevated until the action of the sun upon the surface of the earth has continued long enough to impart a sensible warmth, by which time the moment of sunrise is past, and the sun has risen above the horizontal vapours."

The close observance of natural phenomena by our ancestors, gave rise to many sayings and proverbs, of which several have been presented; and we find another concerning the appearance of the skies that we have just considered.

"An evening red, and morning gray,
Will set the traveller on his way;

But an evening gray, and a morning red,
Will pour down rain on the traveller's head."

The "rainbow," that so frequently adorns and glads the clouded watery heavens, in full display of gorgeouscoloured zones of first-created light, as the token of the covenant between God and man, that the waters

66

shall no more become a flood to destroy all flesh," must be esteemed as the most beautiful and magnificent atmospheric phenomenon that we behold throughout the Four Seasons of the revolving year.

This phenomenon, however, does not admit of explanation through the medium of Chemistry, its interpretation belongs to the very highest departments of the science of Optics, and there probably we only know it in part; but even such part, if it could be here admitted, would more than occupy the remaining limits that are assigned for the actual chemical phenomena of Autumn and Winter.

But we are inevitably led for a few moments to quit the direct province of Chemistry, and trespass upon that of Optics, for unfolding the probable physical cause of the rainbow, in concise and intelligible terms.

The rainbow invariably appears in that part of the heavens which during the day is directly opposite to the sun, and whilst rain is falling between the dark clouds in the one quarter, and the solar beams in the other; these, under most circumstances, impinging upon pellucid drops of water, will either directly pass through them in right lines, or if refracted from such course, they will, upon emerging from the drops, immediately resume it, and pass onward as colourless light.

Under certain natural conditions, which merely to facilitate our inquiry may for the moment be called extraordinary, the solar rays impinging upon drops of water, will not only pass through them, or be simply

refracted, as above, but upon emerging from the drops, a portion of the rays will continue to pass onward as colourless light after ordinary refraction; whilst another portion deviates from such path, and is further refracted, or broken, into seven extraordinary-coloured rays, or prismatic rays, as mentioned at page 23 of the Introductory Chapter.

This extraordinary or coloured refraction or analysis of solar light, is frequently presented by drops of morning dew, but in greater perfection by drops of rain, in falling through the atmosphere, between a dark cloud and the brilliant sun, the rays of which entering and emerging from successive drops, are refracted into Violet light, which departs farthest from the path that the unaltered rays would have pursued, and into Red light, which keeps nearest the path that the unaltered rays would have pursued; thus the external and the internal fringes of the rainbow are formed, and they include within their zones the remaining coloured rays in the order of their inherent refrangibility, the Indigo, Blue, and Green, being nearest the Violet, whilst the Yellow, and Orange, are nearest the Red; thus presenting a perfect rainbow of the seven colours of analysed light.

Or in more technical terms, the Violet, Indigo, Blue, and Green, rays, are the most refrangible, whilst the Yellow, Orange, and Red, are the least refrangible rays of solar light; the rainbow, therefore, is said to present a magnificent natural example of its analysis; for the coloured rays cannot be divided into others.

When a single and perfect rainbow appears, its interior fringe is Red, and its exterior fringe is Violet ; but a "double rainbow" is most frequent; a phenomenon that is, of one bow within another; and then not only are the colours of the inner and smaller, or Primary bow, more vivid than those of the outer and larger, or Secondary bow, but they are exactly in the reverse order, the interior fringe of the inner bow being Violet, and its exterior fringe being Red.

The form of the "double rainbow" the artist has successfully represented in the above engraving, the dark shading of the bows denoting their respective fringes of violet light, as the employment of surfaces to reflect individual colours is impracticable in this department of art; indeed, when we consider that the effect of an engraving depends upon the total reflection of one portion of colourless light, by the surface

of the paper, and the total absorption of another portion by the surface of the ink, it becomes extraordinary that simple engravings should convey to the eye any correct notion of the appearances of surrounding objects.

"

The following ancient and popular proverb concerning the rainbow," affords one more example of a refined physical truth appearing in plain homely guise :

"A rainbow in the morning, is the shepherd's warning, A rainbow at night, is the shepherd's delight."

"This old proverb is generally correct, as a rainbow can only occur when the clouds containing or depositing the rain are opposite to the sun; and in the evening the rainbow is in the East; and in the morning in the West; and as our heavy rains in this climate are usually brought by the westerly wind, a rainbow in the West indicates that the bad weather is on the road by the wind to us; whereas the rainbow in the East proves that the rain in the clouds is passing from us."

"As an indication of wet weather approaching, nothing is more certain than a halo round the moon, which is produced by the precipitated water, and the larger the circle, the nearer the clouds, and consequently the more ready to fall."

All things demand equal attention from him who truly loves and desires knowledge; thus the foregoing explanation of the homely proverb emanated from the