Amongst the most curious instances of absorption is that which is uniformly discovered in the solar spectrum, particularly when we examine it with a telescope. We then find that the coloured rays are crossed by a great number of dark bands or lines, giving no light; these are generally called Fraunhofer’s dark lines, as it was to the indefatigable exertions of that experimentalist, and by the aid of his beautiful instruments, that most of them were discovered and measured, and enumerated, although they were previously noticed by Dr. Wollaston. It is quite clear that those lines represent rays which have been absorbed in their passage from the sun to the earth: although some of them have no doubt undergone absorption within the limits of the earth’s atmosphere, we have every reason to believe, with Sir John Herschel, that the principal absorption takes place in the atmosphere of the sun.[89] It has been proved by Dr. Miller, that the number of those dark lines is continually varying with the alteration of atmospheric conditions;[90] and the evidences which have been afforded, of peculiar states of absorption by the gaseous envelope of the earth,--during the prosecution of investigations on the chemical agencies of the sun’s rays,--are of a sufficiently convincing character. It has been calculated by Bouguer, that if our atmosphere, in its purest state, could be extended rather more than 700 miles from the earth’s surface instead of nearly 40, as it is at present, the sun’s rays could not penetrate it, and this globe would roll on in darkness and silence, without a vestige of vegetable form or of animal life. In the Hebrew version of the Mosaic History, the reading is, “Let light appear:” may not this really mean that the earth’s atmosphere was so cleared of obstructing vapours, that the solar rays were enabled to reach the earth? The same calculation supposes that sea-water loses all its transparency at the depth of 730 feet; but a dim twilight must prevail much deeper in the ocean. The researches of Professor Edward Forbes have proved, that at the depth of 230 fathoms in the Ægean sea, the few shelled animals that exist are colourless: no plants are found within that zone; and that industrious naturalist fixes the zero of animal life of those waters at about 300 fathoms.[91] Since these zones mark the rapidly diminishing light, it is evident that where life ceases to be must be beyond the limits to which life can penetrate. Our atmosphere, charged with aqueous vapour, serves to shield us from the intense action of the solar powers. By it we are protected from the destructive influences of the sun’s light and heat; enjoy those modified conditions which are most conducive to the healthful being of organic forms; to it we owe “the blue sky bending over all,” and those beauties of morning and evening twilight of which ---- Sound and motion own the potent sway. Responding to the charm with its own mystery.