CHAPTER X. THE ATOMIC THEORY FROM SIR ISAAC NEWTON TO JOHN DALTON. "To trace in Nature's most minute design The Invisible in things scarce seen revealed, HE foregoing chapter offers an outline of the efforts made by the ancients to comprehend the nature of the cosmos on the basis of atoms. The same groundwork materially influenced the speculative philosophy that long, and almost lastingly, ruled the direction of modern thought, that is seen cropping out from time to time in the hands of the Cartesians and other metaphysicians and physicists; and exercising more or less jurisdiction from the days of the poetic Lucretius down to the author of the "Principia." "The chemical atoms" may have passed across the mental vision of Geber and the polypharmists, but any recognition of their apparent nature dates no further back than the year 1777, when Wenzel in part indicated the law of reciprocal proportion; and can only be said to have attained scientific place in 1803, 'when Dalton propounded the essentials of his atomic theory. To the mind of the observant reader the question will ere this have occurred, "What is an atom like? -its size, configuration, and affinities; its history, in short?" To meet such interrogations the greatest intellects of every age have devoted their energies; yet, with all their mental discernment, backed by most ingenious appliances, Nature cannot be made to disclose her arcana, much less to present herself in the nude form that would afford demonstration or conviction to the uninitiated. It may be stated in limine, and with a frank admission of our imperfect knowledge of the status quo of atoms, that inference and hypothesis guide chemists in their discussions on those infinitesimal units or particles of matter. Byand-by, however, it will be made apparent that the framing of the atomic hypothesis is not only justifiable, but found to be in accordance with both the phenomena and the facts falling within the operations of the chemist. To give the amateur in science a notion of the minute, marvellously minute, conditions in which Nature carries on her mysterious work, a few facts may be adduced in the hope of affording him a certain amount of insight into the outer world of molecular atoms; be these atoms viewed as parts of the gaseous atmosphere, or as dense liquids, or as the more solid constituents of the organic and inorganic worlds. The air we breathe is like a vast ocean trembling with invisible waves, of which no more tangible idea can be formed than that elicited by watching the finest dust of a sunbeam; that dust consisting of dark molecules, or aggregate masses of atoms floating amid the purer ether pervading space. A Sketch of the Atomic Theory. 183 Everybody is familiar with the sting of a nettle, but few persons have examined by means of a lens the delicate hairs on the leaf of the nettle, from which the tiniest of drops escapes, the insertion of which within the human skin causes heat, redness, and irritation. But what is this irritating fluid compared with the deadly poison of prussic acid, a minim or full drop of which, in its pure, anhydrous* state, causes death in a few seconds! Here is a strange subtlety of action that can arrest pulsation and life at once, yet all its virus is to be found in a single drop of transparent fluid! This instance of the extreme potential of force clothed in a liquid globule is rivalled in character by the revelations of the microscope displaying to us a world of minutiæ, of organic beauty throughout. Turning to animal life, the microscope in the hands of Ehrenberg disclosed animalcules so infinitesimal in size that a single drop of water was computed to contain 500,000,000 of them. Here was not only a picture of a universe of atoms, but the living proof of a universe of organic beings equal in number to the entire human population on the surface of the globe! In the fossil world geologists have traced a whole system of rocks (these calcareous masses in England * The anhydrous or pure prussic acid is only to be seen, and that very rarely, in the hands of the scientific chemist or experimental physiologist. The medicinal prussic acid only contains about three per cent. of this anhydrous acid. The potency of the pure acid, and its general toxicological and therapeutical history, constituted my graduation thesis, an abstract of which will be found in the Edinburgh Quarterly Medical and Surgical Journal, January 1839. being about a thousand feet deep) composed entirely of the shells of siliceous animalcules; yet so small are these débris of a former world of organic life, that a single chalk-enamelled card of my Lady Fashionable form a zoological cabinet of perhaps a hundred thousand shells! The dark spot on a soap-bubble, just before it bursts, cannot exceed 100000th part of an inch in thickness; yet even this is composed of many strata of atoms; for this iridescent film of moisture must consist at least of one atom of soap and one of water. Now, the atom of soap is composed of soda, stearic, margaric, and oleic acids; and the latter of, at least, one molecule of oxygen and one of hydrogen; and each of these possess the essential properties of impenetrability, extension, and figure. Dr Thomson of Glasgow has shown that an atom of lead cannot exceed in weight the 31000000000oth of a grain; and that the sulphur united with it in the form of sulphuret could not be more than 2015000000000th of the same! Goldbeaters by hammering reduce gold to leaves so thin that 360,000 must be laid upon one another to produce the thickness of an inch; and 50700000th of a grain may be distinguished by a common microscope. But the coating of gold on silver lace is still finer, when it is computed that the 1100000000th of a grain, spread out as a distinct layer of gold, may be seen through a good lens. The contemplation of these remarkable proofs of the molecular forms and minutiæ pervading Nature's great plan, may help the reader's belief to a more infinitesimal condition of matter than has been set A Sketch of the Atomic Theory. 185 forth, or is ever likely to be demonstrated; and at the same time tend to promote his sanction of doctrines that chemists have found it needful to frame upon a theoretical consideration of the atomic constituents of bodies. Not only is our planet, in all its granitic framework, and its liquid and aerial construction, built up of indescribably minute particles, or the atoms of the sixty-three elementary substances noted by chemists; but, relying on the observations made by the spectrum analysis, which finds the vapours and the metals of earth in the radiant streaming aurora borealis, and in the central nucleus of comets, it is fair to infer that such also is the construction of the great orbs in the firmament. Such phenomena are of striking interest, as illustrating the structural inorganic analogies pervading the universe, upon which the natural theologian may found an attractive teleological theme, not so striking or convincing in character, perhaps, as one that might be drawn from the contemplation of the organic morphological types so strikingly visible and intelligible to all men of culture and education. The atom in the physical world is like the cell in the biological world-that morphological unit or ultimate element of form out of which all the organs in the living body are built up. As every organised being derives its existence from a sphere of protoplasm and cell-growth, so does every chemical change rest on the fresh arrangement of molecular atoms. The microscope enables the anatomist to define the organic cell in some of its phases; but no one has been able to see or handle a single molecule. Mole |