It is the function of science, not as some think to divest this universe of its wonder and mystery, but, as in the case before us, to point out the wonder and the mystery of common things. Those fern-like forms, which on a frosty morning overspread your windowpanes, illustrate the action of the same force. Breathe upon such a pane before the fires are lighted, and reduce the solid crystalline film to the liquid condition; then watch its subsequent resolidification. You will see it all the better if you look at it through a common magnifying glass. After you have ceased breathing, the film, abandoned to the action of its own forces, appears for a moment to be alive. Lines of motion run through it; molecule closes with molecule, until finally the whole film passes from the state of liquidity, through this state of motion, to its final crystalline repose.
I can show you something similar. Over a piece of perfectly clean glass I pour a little water in which certain crystals have been dissolved. A film of the solution clings to the glass. By means of a microscope and a lamp, an image of the plate of glass is thrown upon the screen. The beam of the lamp, besides illuminating the glass, also heats it; evaporation sets in, and at a certain moment, when the solution has become supersaturated, splendid branches of crystal shoot out over the screen. A dozen square feet of surface are now covered by those beautiful forms. With another solution we obtain crystalline spears, feathered right and left by other spears. From distant nuclei in the middle of the field of view the spears shoot with magical rapidity in all directions. The film of water on a window-pane on a frosty morning exhibits effects quite as wonderful as these. Latent in these formless solutions, latent in every drop of water, lies this marvellous structural power, which only requires the withdrawal of opposing forces to bring it into action.
The clear liquid now held up before you is a solution of nitrate of silver — a compound of silver and nitric acid. When an electric current is sent through this liquid the silver is severed from the acid, as the hydrogen was separated from the oxygen in a former experiment; and I would ask you to observe how the metal behaves when its molecules are thus successively set free. The image of the cell, and of the two wires which dip into the liquid of the cell, are now clearly shown upon the screen. Let us close the circuit, and send the current through the liquid. From one of the wires a beautiful silver tree commences immediately to sprout. Branches of the metal are thrown out, and umbrageous foliage loads the branches. You have here a growth, apparently as wonderful as that of any vegetable, perfected in a minute before your eyes. Substituting for the nitrate of silver acetate of lead, which is a compound of lead and acetic acid, the electric current severs the lead from the acid, and you see the metal slowly branching into exquisite metallic ferns, the fronds of which, as they become too heavy, break from their roots and fall to the bottom of the cell.
These experiments show that the common matter of our earth — 'brute matter,' as Dr. Young, in his Night Thoughts, is pleased to call it — when its atoms and molecules are permitted to bring their forces into free play, arranges itself, under the operation of these forces, into forms which rival in beauty those of the vegetable world. And what is the vegetable world itself, but the result of the complex play of these molecular forces? Here, as elsewhere throughout nature, if matter moves it is force that moves it, and if a certain structure, vegetable or mineral, is produced, it is through the operation of the forces exerted between the atoms and molecules.
The solid matter of which our lead and silver trees were formed was, in the first instance, disguised in a transparent liquid; the solid matter of which our woods and forests are composed is also, for the most part disguised in a transparent gas, which is mixed in small quantities with the air of our atmosphere. This gas is formed by the union of carbon and oxygen, and is called carbonic acid gas. The carbonic acid of the air being subjected to an action somewhat analogous to that of the electric current in the case of our lead and silver solutions, has its carbon liberated and deposited as woody fibre. The watery vapour of the air is subjected to similar action; its hydrogen is liberated from its oxygen, and lies down side by side with the carbon in the tissues of the tree. The oxygen in both cases is permitted to wander away into the atmosphere. But what is it in nature that plays the part of the electric current in our experiments, tearing asunder the locked atoms of carbon, oxygen, and hydrogen? The rays of the sun. The leaves of plants which absorb both the carbonic acid and the aqueous vapour of the air, answer to the cells in which our decompositions took place. And just as the molecular attractions of the silver and the lead found expression in those beautiful branching forms seen in our experiments, so do the molecular attractions of the liberated carbon and hydrogen find expression in the architecture of grasses, plants, and trees.
In the fall of a cataract and the rush of the wind we have examples of mechanical power. In the combinations of chemistry and in the formation of crystals and vegetables we have examples of molecular power. You have learned how the atoms of oxygen and hydrogen rush together to form water. I have not thought it necessary to dwell upon the mighty mechanical energy of their act of combination; but it may be said, in passing, that the clashing together of 1 lb. of hydrogen and 8 lbs. of oxygen to form 9 lbs. of aqueous vapour, is greater than the shock of a weight of 1,000 tons falling from a height of 20 feet against the earth. Now, in order that the atoms of oxygen and hydrogen should rise by their mutual attractions to the velocity corresponding to this enormous mechanical effect, a certain distance must exist between the particles. It is in rushing over this that the velocity is attained.
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This idea of distance between the attracting atoms is of the highest importance in our conception of the system of the world. For the matter of the world may be classified under two distinct heads: atoms and molecules which have already combined and thus satisfied their mutual attractions, and atoms and molecules which have not yet combined, and whose mutual attractions are, therefore, unsatisfied. Now, as regards motive power, we are entirely dependent on atoms and molecules of the latter kind. Their attractions can produce motion, because sufficient distance intervenes between the attracting atoms, and it is this atomic motion that we utilise in our machines. Thus we can get power out of oxygen and hydrogen by the act of their union; but once they are combined, and once the vibratory motion consequent on their combination has been expended, no further power can be got out of their mutual attraction. As dynamic agents they are dead. The materials of the earth's crust consist for the most part of substances whose atoms have already closed in chemical union — whose mutual attractions are satisfied. Granite, for instance, is a widely diffused substance; but granite consists, in great part, of silicon, oxygen, potassium, calcium, and aluminum, whose atoms united long ago, and are therefore dead. Limestone is composed of carbon, oxygen, and a metal called calcium, the atoms of which have already closed in chemical union, and are therefore finally at rest. In this way we might go over nearly the whole of the materials of the earth's crust, and satisfy ourselves that though they were sources of power in ages past, and long before any creature appeared on the earth capable of turning their power to account, they are sources of power no longer. And here we might halt for a moment to remark on that tendency, so prevalent in the world, to regard everything as made for human use. Those who entertain this notion, hold, I think, an overweening opinion of their own importance in the system of nature. Flowers bloomed before men saw them, and the quantity of power wasted before man could utilise it is all but infinite compared with what now remains. We are truly heirs of all the ages; but as honest men it behoves us to learn the extent of our inheritance, and as brave ones not to whimper if it should prove less than we had supposed. The healthy attitude of mind with reference to this subject is that of the poet, who, when asked whence came the rhodora, joyfully acknowledged his brotherhood with the flower
Why thou wert there, O rival of the rose!
I never thought to ask, I never knew,
But in my simple ignorance supposed
The self-same power that brought me there brought you.
Emerson.