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passage occurs: it is quoted for the purpose of showing that the above views have not been hastily adopted, and to give the origin of the term ACTINISM, which has been almost universally adopted :

“The science of Thermotics (Whewell), or of Thermochroology (Melloni), is considered of sufficient importance to have its nomenclature; and M. Melloni, in a paper published in the Bibliothèque Universelle de Génève,' October, 1841, has entered very fully into the matter. It is therefore essential to the successful prosecution of our inquiries that the third class of phenomena, which we have been particularly engaged in the consideration of, should have a term by which it might be distinguished. Sir John Herschel, in his memoir “On the Chemical Action of the Rays of the Solar Spectrum,' used the epithet Actinograph to indicate an instrument of a very ingenious kind, devised by him for registering the different degrees of chemical power accompanying the solar Light during the day. .... We might therefore, upon the strength of this authority, adopt the substantive exti (ray), and give some compound term formed from this radical to indicate this principle accompanying the other solar rays. There is, it must be admitted, some difficulty involved in the adoption of such a term, as it will apply to any radiant power, whether Light, Heat, or Photographic energy.”—Under this impression, I proposed to adopt such a term as svecanuece, ENERGEMA (energy), which was slightly modified and converted into ENERGIA, to which it was thought, if desirable, the substantive ray, for the purpose of expressing the agent more correctly, might be prefixed, thus making ACTINERGIA.

At the meeting of the British Association at York, the value of this term was discussed. Sir John Herschel had communicated a paper designated as “ Contributions to Actino-Chemistry," which he spoke of as “the newlycreated science;" and it was thought advisable by several members of the Chemical Section to adopt the term AC

TINISM instead of energia, when desiring to speak of the chemical power of the sunbeam.

It may be necessary to remark, that the chemical powers belonging to Light and HEAT are scarcely to be confounded with ACTINISM. Light does, by exciting vitality in living organisms, produce chemical decomposition; and there is reason for believing that on dead organic matter Light acts chemically, but never on inorganic masses. HEAT, as a radiant force, also produces changes of a peculiar kind, which will be fully described; but these are broadly distinguished from the effects produced by ACTINISM. These remarks and this explanation of my views were thought necessary, owing to the severity with which my opinions have been judged : I have only now to submit them and the following “Researches” to the judgment of the reader, premising that I am quite prepared to resign the views advocated, the moment one conclusive experiment has been arrived at in support of the view that Light is the chemical agent producing Photographic phenomena.

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HISTORY OF THE PROGRESS OF THE INQUIRY UNTIL THE AN

NOUNCEMENT OF THE DISCOVERY OF PHOTOGRAPHY.

(1.) INVOLVED in mystery as every thing connected with the early history of our planet is, it would be entangling the subject with abortive speculations, did I offer any on those passages of the Mosaic history which narrate the creation of Light, and of the orbs of the firmament. We there find Light the creation of the first day; and the Sun, which we are accustomed to regard as the source of Light, or the exciting mover of the luminiferous ether, as the creation of the fourth period. Regarding this, our only record of the beginning, as the true expression of the sequence of events, it does not appear that we are required to interpret this revealed word to our finite apprehensions. The origin of things is lost in the sepulchral darkness of time, into which the eye of the most gifted cannot penetrate. The Pentateuch declares in sublime conciseness, And God said, Let there be Light, and there was Light, Distinguishingly marking the importance of this element in the great system of Nature. The grass, the herb yielding seed, and the fruit-tree yielding fruit, owe their growth, their glowing colours, and their beauty, to the influences of the solar beams. The moving creatures of the waters — the fowl that fly above the earth in the open firmament of heaven - the cattle and the creeping thing

are directly dependent for healthful vigour, and indeed the continuance of life, on this subtile power, which appears to have given form to the chaotic earth, as it chased the darkness from the face of the deep.

(2.) An agent influencing every form of animate and inanimate creation, would necessarily excite the attention of mankind from the earliest periods. As it is by the influence of Light operating through the wonderful me. chanism of the organ of vision, that a most extensive and important class of impressions are made upon the mind of man, he has, from the infancy of his days, regarded its source with feelings of wonder; and the Sun has been the object of his untutored adoration.

(3.) The uncultivated inhabitant of the wilds of nature had his moments of contemplation; and then his thoughts, travelling in the misty labyrinth of ignorance and superstition, shadowed out a great primary cause, to which he referred all the mysteries of that mighty universe of which he found himself a proud inhabitant.

The nomadic tribes of the Caucasian valleys over which spread a luxuriant vegetation, and an excess of life, could not but observe the peculiar obedience of organised creation to the influences of the changing seasons. The pastoral state was peculiarly adapted for the cultivation of those powers of the mind which elevate the individual or the mass; and in the progress of the shepherd-kings we may trace the dawning of the reign of reason, which eventually gave to a small nation the sovereignty of the known world. Men in this condition could not long remain ignorant of the dependence of all the phenomena of vegetation upon Light. The growth of the plant, the unfolding of the leaf, the formation of the flower, of the fruit and of the seed, were soon found to be under the influence of the orb of day. In spring and summer external nature was seen to grow into strength and beauty, and through autumn and winter to decline, and indeed to die. Some connection between these phenomena and the increasing and declining powers

ANCIENT THEORY OF VISION.

of the sun, at an early period became evident to man; and when the innate consciousness of a creative power was struggling, through the darkness of superstitious ignorance, he, in his simplicity, gave to that orb the attributes of a god. The earliest religions of the Oriental races all bear evidence of this ; and their mythologies, rich in the poetry of Nature, place one deity at the head of their polytheistic systems — the God of Heaven and of Light. In Baal and Astarte-in Zeus and Hera-. in Apollo and Athena — we see alike, impersonations of Light the eternal renovator, and of Nature flourishing and decaying beneath the alternations of its power.

(4.) In the youth of mankind all natural truths were viewed through a veil, which no one dared to draw aside, or dreamed of lifting up. A beautiful poetry overspread creation, and the spirit of life was seen and worshipped in the highest and the lowliest things.

At length a philosophic spirit grew up in the mind of man: he speculated on the mysteries by which he found himself surrounded — involved himself in the mazes of metaphysics; and all his early efforts “ were like the gropings of the blind Cyclops in his cavern;" when searching for the light of truth he too frequently wandered from its shrine.

(5.) It does not appear that the physical phenomena of Light ever received much attention from the ancient philosophers. In their first attempts to explain vision, they gave to the eye a power of projecting material rays, by which the forms and visible qualities of bodies were felt out; but they were at length induced to abandon this absurdity, and adopted the idea of Light as a peculiar medium, through which impressions were made on the eye, but in what manner was left quite undetermined. The heating power of the sun's rays could not escape notice; and the story of the mirrors of Archimides sufficiently proves that considerable attention had been paid to the laws of reflection.

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