wholly, which are then black; with others, the most numerous cases, only in part; and then, that portion of them which is not so absorbed emanates from the substance in the colour which comes from them to our eye.* After having for many years attended to the phenomena of light, I cannot but consider it to be a universally diffused fluid. Thus far the idea would accord with the undulatory theory; but many facts lead me also to conclude that it actually enters into the composition of all or of most substances, and, like heat, becomes a latent part of them.† From these it is extricable, with more or less rapidity, without the interference of the solar ray, as in the burning of all inflammable bodies, when it passes into its active and visible state. When the two liquids of nitrous gas and oil of turpentine burst into a flame on being mixed, without the approach of any fire, I think we see a striking instance of latent and combined light passing suddenly into the free and active state. So when that brilliant blaze occurs on dipping the iron wire into oxygen gas, it seems to be the latent light combined in the gas, evolving from it instantaneously into its visible form. The sun has nothing to do with these phenomena, nor with any of our artificial illuminations. All these may be deemed latent light emerging from its combinations into free and active visibility. Yet most of the Newtonian princi transparent bodies in nature, air and water, when in sufficient thickness, are capable of absorbing a great quantity of light."-Dr. Brewster, Optics, p. 137. *Sir I. Newton "concluded that the colours of natural bodies are not qualities inherent in the bodies themselves, but arise from the disposi tion of the particles of each body to stop or absorb certain rays; and thus to reflect more copiously the rays which are not thus absorbed."-Dr. Brewster's Life of Newton, p. 46. Bodies absorb light in different degrees, in this order : Charcoal, Coal of all kinds, Silver, Black hornblende, Selenite, Mica, Ib. Opt. 137. Dr. Brewster expresses the same idea, with which I have been for some time impressed: Whatever be the difficulties which attach to the theory that supposes light to consist of material particles, we are compelled by its properties to admit, that light acts as if it were material; and that it enters into combinations with bodies, in order to produce the effects which we have enumerated."--Life of Newton, p. 90. 1- One of the most curions properties of dodies is thed power of alwortung light. Charcoal is the most absorptive of all. Even the most ples and laws concerning it are confirmed by the phenomena which suggested them; and so is much of the new system by those facts which have been adduced in its support.* Hence it is most probable that both theories have a foundation in truth, but require some further additions and modifications on each side to make them consistent with each other; and to remove the apparent contradictions which now keep them in the state of controversial hostility.t There is another grand operation in the formation of material and inorganic nature, which has only become a subject of peculiar study within the last fifty or sixty years, and with which, I think, the yet unknown agencies of LIGHT * Dr. Brewster has very ably distinguished the parts of the Newtonian doctrine of colours, which have been found strictly true, from those which later observations have disproved, and has added his own intelligent views of the new principles that have since been disclosed.--Life of Newton, chap. 7. To our more correct knowledge of light he has himself largely contributed. † We may again notice here the surprising demands which philosophy sometimes makes on the believing principle within us, and the willing credulity with which we receive its annunciations, while we erect ourselves so pugnaciously against the subjects of religious faith. Can any thing of this latter description more exceed our comprehending faculties, or more intensely press our believing ones, than what three men of great science and celebrity, Mr. Herschel, Dr. Young, and Dr. Brewster, with many similar collaborateurs, assure us to be true. I will state it in the words of the first, and add Dr. Young's illustrating calculations. "Modern optical discoveries have disclosed, that every point of a medium through which a ray of light passes is affected with a succession of periodical movements, regularly recurring at equal intervals; no less than 500 millions of millions of times in a single second. It is by such movements communicated to the nerves of our eyes, that we see." --J. W. HERSCHEL'S Discourse, p. 24. Thus Dr. YOUNG tells us, that when we see the following colours, our eyes are affected in a second; that is, in one swing of a pendulum, or while we can pronounce one : In Red, 482 millions of millions of times; In Yellow, 542 ditto ditto ditto; In Violet 707 ditto ditto ditto. Lect. Nat. Phil. vol. ii. p. 627. Dr. Brewster gives the numbers from Mr. Herschel with a little variation, as if after a more exact reconsideration: thus Red...... 477,000,000,000 | Blue..... 622,000,000,000 Undulations in a second. Which exacts more of our faith, religion or philosophy? I think very often the latter. Why, then, more difficult in the one than in the other? are principally concerned. This is CRYSTALLIZATION.* It is that force or agency by which the constituent particles of bodies are united together into certain primitive forms, which all minerals, on being properly broken, are found to exhibit, and which become the rule and basis for the formation of the mass.† Similar figures are made on the primitive one; and of all these accumulated crystals the substance is composed, and into these it can always, by careful labour, be divided. They have been traced to four fundamental forms;◊ and these have been thought to be reducible to one constant and primitive original. We cannot at present say that all bodies are thus crystallized, as some appear without such a state, or with such an imperfect crystallization as to make the agency questionable as to them.¶ Yet this principle seems to be a universal law in the composition of material things.** Like the rest of nature, its formation is perfectly scientific,†† and light seems to be one * "The genius of HAUY discovered the general fact that minerals could be cloven or split in such directions as to lay bare their peculiar, primitive, or fundamental forms."-Herschel's Disc. p. 79. "They are layers of cubic stones laid horizontally one on the other, decreasing regularly in size from the bottom to the top."-Ib. 240. ‡ Mr. Daniel, in his late lectures, showed that these bodies cannot be broken in any way we please, but only in certain particular directions. All the regular solid figures may be made up by piling together pieces of a regular figure, though not one resembling their compound form.Athenæum, 23d Ap. 1831. Germar admits only four fundamental systems, which he names the tesseral, pyramidal, prismatic, and hexagonal: but each of these he divides into two series,-the homoedric and the hemiedric crystals.-Bull. Un. 1830, p. 211. We may see a formation of this sort on melting zinc. A crystalline substance runs from it, which is perfectly crystallized in hexagonal prisms, terminated by pyramids with six faces. These crystals are produced by nature itself-are transparent-of an amber colour, and nearly as hard as steel.-Ib. p. 125. "The division of bodies into crystallized and uncrystallized, or imperfectly crystallized, is one of most universal importance. Almost all the phenomena produced by those natural causes which act within small limits on the immediate mechanism of solid substances are remarkably modified by their crystalline structure."-Hersch. p. 243. Dr. Wollaston believed that the atoms of crystals were spherical, or at least spheroidal. b. p. 125. **"Every chymical compound susceptible of assuming the solid state assumes with it a determinate crystalline form."-Hersch. p. 293. "The crystalline form is in the highest degree geometrical."— Hersch. p. 291. |