Page:Popular Science Monthly Volume 46.djvu/522

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seems to me to be the highest field for the exercise of our intellectual faculties, for it includes ethics on the one hand and psychology on the other, both together constituting the phenomena of mind, while the visible results are conditioned by the attributes of matter. But to-night I propose to begin on a much lower plane, and to attempt only the suggestion of one or two simple laws which are common to nonliving structures, to living beings, and to an organized society.

Since the metamorphoses of matter are endless in number and infinite in succession, let us limit the word "change" to some fixed and definite alteration, such as the burning of an ounce of gunpowder, the falling of the water of Lake Erie over the cliff at Niagara, or the duration of a human life from infancy to old age. In this restricted sense physicists and chemists have recognized two kinds of changes: first, those which tend to go on indefinitely until all the matter present has suffered the alteration in question; second, those which give rise to products which are unfavorable to the original forces at work such changes are self-limited and may cease, therefore, long before all the material has been used. As an example of the first type—that of unlimited change—I may again cite Niagara, for here the falling water sets up no reaction against itself. This is the popular idea of a change, because we seem to be surrounded only by such cases.

The falling snow or rain, the uprooting of trees by a whirlwind, the constant streaming away of light from a lamp or heat from a stove, with the concomitant burning of fuel, all are familiar experiences and they are unlimited in character. But while these and others like them have served to stamp the word "change" with a definite meaning in the mind of the public, it is because they seem the only types to a superficial observation. In reality, however, the other kind, the self-limited changes, are vastly more numerous. Take as an example the freezing of water: the moment ice is formed it acts as a partial nonconductor, or blanket, to keep heat from escaping, and so the rate of freezing is diminished, and here in our climate is wholly stopped when a thickness of two feet of ice is reached. Or, again, consider the case of an elastic body on which a weight is placed. If it is a spring, it will bend, and finally, if the weight is not too great, will reach a position where the latter is just supported. This equilibrium is brought about by the internal stress of resilience of the spring acting against the force of gravity, and thus the change in position of the weight-has called forth a power which is the result of that change, and at the same time limits it in amount.

While this illustration is an elementary one, it is for all that exceedingly important, because it is so common; it covers every