The task of developing the progress of the science of Optics, is not that to which we have to direct attention. That extraordinary property of the solar beam, by which chemical changes of the most singular kind are brought about, in living and in dead matter, in organic and inorganic bodies, is the sole subject of investigation.

(6.) Although the most ordinary observer must, through all time, have noticed that the sun's rays weakened and even destroyed some colours, while others were darkened by their influence, yet these facts excited no attention; and it was reserved for the philosophers of our own time to show, that the study of this peculiar property of the Sunbeam tends to improve our perceptions of the beautiful, and leads to the discovery of some of the most important truths connected with the secret operations of organisation.

(7.) At an early period the beauty of crystalline gems attracted attention; and, being used, then as now, extensively for the purpose of adorning the person, the search for diamonds, rubies, and sapphires was often a very lucrative employment. As some of these precious stones were said to possess the property of shining in the dark, and as most of them refract the luminous rays with extraordinary brilliancy, it became a matter of conjecture if they shone with their own light, or if it was, that they again poured out light which they had the power of absorbing. Several Italians and others wrote on this subject, amongst whom Boetius de Boot was distinguished by his freedom from the philosophy of the schools; and we find him saying, "No man ever durst aver he had actually seen that stone that of itself afforded light." That eccentric and extraordinary genius Benvenuto Cellini, however, affirms, in his Treatise on Jewellery, that he has seen the carbuncle glowing like a coal with its own light. The only advantage gained by this discussion was, that it led some to endeavour to prepare substances which should possess the property of emitting light in the dark; and curiosity was at

ALCHEMICAL HYPOTHESIS.

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length gratified by the discovery of the Phosphorus hermeticus, of Balduinus, of the Bolonian Stone, and several of the phenomena of phosphorescence.

(8.) Amidst all the error and charlatanry of the alchymists, we find many important observations and some really great discoveries. Amongst these empirical philosophers were men gifted with minds of a superior order, and the exceedingly careful experiments made by them, whilst they were endeavouring to torture the base metals into gold, and to distil the Elixir Vitæ, became the guiding lights to modern science. In 1556 it was noticed that horn silver (chloride of silver fused) was blackened by the sun's rays. This and other peculiar influences which the alchymists observed, led them to fancy that the "sulphurous principle" of Light was one of the most important agents in giving to Nature her infinite variety of form. Possessed with the idea, borrowed from the ancients, that all matter was compounded of three or four simple elements, many of these experimentalists regarded Light as the great primary cause, which modified their salt, sulphur, and mercury, and transmuted them into the earths and metals, or the myriad forms of organic matter. A notion, indeed, somewhat similar to this prevailed amongst the ancient philosophers, for Democritus speaks of minute atoms in swift motion, which, by their smallness and rapidity, were able to permeate the hardest bodies.

(9.) "The sun's rays," Homberg at a much later period says, "will insinuate themselves into bodies so as greatly to increase their weight;" and he seriously relates that four ounces of Regulus Martis, in powder, were augmented by in the balance, by being exposed for an hour at the distance. of a foot and a half from the focus of the Duke of Orleans' burning-glass, notwithstanding much of it was dissipated in smoke: the absorption of oxygen was, of course, unknown to the ingenious Homberg. It will be interesting to review a few more of his assertions connected with this part of the subject. "A perfect metal," he writes, "is

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nothing but very pure mercury, whose small particles are every way pierced and filled with the sulphureous principle, or the matter of Light, which links and binds the whole mass together." "Gold differs from silver in nothing but in having the globules of the mercury, whereof it consists, penetrated through and through, and being more fully saturated with the sulphureous principle of the rays of Light." "The Light of the sun," he continues, impinging against terrestrial bodies, modifies them according to their several textures; the luminous matter insinuates itself into the substance of bodies, to produce their sulphur, changes the arrangement of their parts; increases them, and consequently alters the substance of the body itself, after as many different manners as in different quantities it can be differently placed. So that, would we compare the variety of the materials which exist with those which might be brought into being, by all the combinations possible to be made, we must say that the universe, so far as we know of it, is but very small in comparison of what it might be; and that if there were several worlds, formed like this of ours, they might all be differently furnished with objects, without changing either the manner or the matter of the bodies whereof they should consist; which demonstrates an infinite contrivance and power in the Being who made the universe."*

(10.) Amidst the incorrect views of Homberg, the result of working with one idea, there continually breaks forth a fine philosophy; and we find the illustrious Newton entertaining a similar view to that just quoted, but he lends to the speculation all that refinement which distinguishes every effort of his master mind. Sir Isaac Newton demands, whether "gross bodies and Light are not convertible into one another; and may not bodies receive much of their activity from the particles of Light which enter into their composition? For all fixed bodies, being

* French Memoirs, from 1700 to 1705.

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heated, emit Light so long as they remain sufficiently heated; and Light mutually stops in bodies as often as its rays strike upon their parts."

The hypothesis of Homberg, and the question of Newton, both exhibit striking proofs of remarkable penetration, and afford evidence of minds struggling to burst through the materialities which empiricism had crowded around the science of their times. The hypothesis of the alchymist has been exalted into a probable theory by the discoveries of the modern chemist: and when we reflect that the question asked by Newton remains still unanswered, we should restrain the railroad speed of the science of our day, gliding as it does too commonly over the easiest paths, and viewing in its rapid transit the surface of nature merely.

(11.) I cannot quit this part of my subject without referring to some of the speculations of the talented, though credulous Boyle. I do this, not with any idea of supporting his views, which I regard as being, to a certain extent, visionary, but for the purpose of showing, that long before inductive science had proved the chemical agencies of the different rays of the prismatic spectrum, the curiosity of a gifted mind had advanced very nearly to the truth. In the "Memoirs for a General History of the Air," we find the following remarkable passages, which, although to a certain extent an apology for astrology, are full of suggestions; and, to use Boyle's own words, "wholly to neglect the physical use of the motion of these bodies (the planets), because superstition has crept in, is very extravagant, and ought not to pass uncensured in men of learning."

"Thus every planet," Boyle writes, "has its own proper Light distinct from that of the others, which is either a bare quality, and then its utmost use and design is only to illuminate, or else all Light is attended with some peculiar power, virtue, or tincture; whence 'tis plain that every Light has its peculiar property, tincture, and colour - its own specific virtue and power, wherein the planets differ

from each other; and consequently the celestial bodies are not to be considered as sluggish and unorganised matter, but as full of their proper motion, operation, and life. Thus the sun not only shines upon all the planets, but by his genial warmth calls forth, excites, and raises the motions, properties, and powers peculiar to them whence, according to the angle they make with that grand luminary, and the degree wherein they are enlightened, either by its direct or oblique rays, in a near or remote situation in respect of the earth, must be more or less perceived by us. As for the manner wherein the planets transmit their powers, and thereby affect the remote bodies, 'tis not difficult to apprchend it; for we affirm no virtue or power to flow from the planets that comes not along with the Light as a property thereof." The correctness of the following has been strikingly confirmed by the researches of Faraday on magnetic force, and the investigations of Sabine on the phenomena of terrestrial magnetism.

"As the other planets, so also our earth, is not only enlightened, warmed, cherished, and made fruiful by the power, virtue, and influence of the sun, but it hath, moreover, its proper, magnetical, planetary force awakened, fermented, excited, and agitated, which it sends back with the reflected Light of that luminary."*

In the same Memoirs, Boyle notices the Oriental tradition, that the rays of the moon produce a baleful effect upon persons exposed asleep to their influence. I may here remark that the popular notion of timber trees being materially influenced by the Light of the moon appears, from a very early period, to have been a generallyreceived idea; and the Honduras mahogany trees are cut by the natives at a particular period of the moon's age.

(12.) Notwithstanding that many of those remarkable phenomena which were supposed to be dependent upon some peculiar principle of Light were curiously observed,

* Boyle's Works, vol. iii. p. 39.