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JANUARY, 1904.

No. 3.




In the seventh book of the Republic of Plato* occurs the following passage:

“Imagine a number of men living in an underground cavernous chamber, with an entrance open to the light, extending along the entire length of the cavern, in which they have been confined, from childhood, with their legs and necks so shackled, that they are obliged to sit still and look straight forward, because their chains render it impossible for them to turn their heads round; and imagine a bright fire burning some way off, above and behind them, and an elevated roadway passing between the fire and the prisoners, with a low wall built along it, like the screens which conjurers put up in front of their audiences, and above which they exhibit their wonders. Also figure to yourself a number of persons walking behind the wall, and carrying with them statues of men and images of other animals, wrought in wood and stone and all kinds of materials, together with various other articles, which overtop

* Golden Treasury edition, pp. 235, 236.

the wall; and, as you might expect, let some of the passers-by be talking, and the others silent.

"Let me ask whether persons so confined could have seen anything of themselves or of each other, beyond the shadows thrown by the fire upon the part of the cavern facing them? And is not their knowledge of the things carried past them equally limited? And if they were able to converse with one another, would they not be in the habit of giving names to the objects which they saw before them? If their prison house returned an echo from the part facing them, whenever one of the passers-by opened his lips, to what could they refer the voice, if not to the shadow which was passing? Surely such persons would hold the shadows of those manufactured articles to be the only realities."

With reference to our absolute knowledge of the phenomena of nature, this splendid comparison is as correct today as it was in the days of Plato, about 400 B. C.; we are only as prisoners in a great cave, watching shadows of passing objects thrown upon the cavern wall, and reflecting upon the real natures of the things whose shadows we see. We know things only by their effects; the essential nature of matter and energy is far from our understanding.

In early and mediaeval times, the recognition of the fact that nature in its ultimate form is unknowable, led to many harmful superstitions. Chief among the fallacies of the early ages was the belief that God at will could, and did, cause various phenomena to appear in nature, which might be contrary to all human experience. As observed in the last article, a class of men arose who claimed to be in possession of knowledge which made them also able, at will, to cause various supernatural manifestations. Thus arose the occult sciences, so called, alchemy, astrology, magic, witchcraft, and all other similar abominations of the intellect. Such beliefs made the logical study of nature superfluous, for any apparent regularity or law in nature might at any time be overturned by a person in possession of a formula of the black art or a properly treated broomstick.

While such ideas prevailed among the majority of men, the rational study of science could make little progress. In the march. of the ages, as the ideas of men were classified, it began to be un

derstood that the claims of the devotees of the mystical arts not only could not be substantiated but were in direct opposition to the known operations of nature. It became clear to the truthseekers, that in nature a given cause, acting upon any given object, providing all surrounding conditions be left unchanged, will always produce the same effect. Thus, coal of a certain quality, brought to a high temperature in the presence of air, will burn and produce heat; a stick held in water at the right angle will appear crooked; iron kept in contact with moisture and air, at the right temperature, will be changed into rust; sunlight passed through a glass prism will be broken into rainbow colors; ordinary plants placed in a dark cellar will languish and die. No matter how often trials are made, the above results are obtained; and today it is safe to assert that in the material world no relation of cause and effect, once established, has failed to reappear at the will of the investigator. As this principle of the constancy in the relation between cause and effect was established, the element of chance in natural phenomena, with its attendant arts of magic, had to disappear. It is now well understood by intelligent persons that the law of order controls all the elements of nature.

It is true that the cause of any given effect may, itself, be the effect of other causes, and that the first cause of daily phenomena is not and probably cannot be understood. It is also true that very seldom is the mind able to comprehend why certain causes, save the simpler ones, should produce certain effects. In that respect we are again nothing more than Plato's cave prisoners, seeing the shadows of ultimate realities. However, the recognition of the principle of the invariable relation between cause and effect was a great onward stride in the intellectual development of the world.

Now, as men began to investigate nature with her forces, according to the new light, numerous relations of the forces were discovered in number far beyond the comprehension of the human mind. Then it was found necessary to group all facts of a similar nature, and invent, if possible, some means by which the properties of the whole group might be stated in language so simple as to reach the understanding. Thus came the laws of nature.

For instance, men from earliest times observed the heavenly bodies and the regularity of their motions. Theories of the uni

verse were invented which should harmonize with the known facts. As new facts were discovered, the theories had to be changed and extended. First it was believed that the earth was fixed in midspace, and sun and stars were daily carried around it. Hipparchus improved this theory by placing the earth not exactly in the center of the sun's circle. Ptolemy, three hundred years later, considered that the sun and moon move in circles, yearly, around the earth, and the other planets in circles, whose centers again described circles round the earth. Copernicus simplified the whole system by considering that the earth rotated around its axis, and around the sun. Keppler next showed that the earth moved around the sun in certain curves termed ellipses. Finally, Newton hit upon the wide-embracing law of gravitation, which unifies all the known facts of astronomy.* All the earlier laws were correct, so far as they included all the knowledge of the age in which they were proposed, but were insufficient to include the new discoveries.

Laws of nature are, therefore, man's simplest and most comprehensive expression of his knowledge of certain groups of natural phenomena. They are man-made, and subject to change as knowledge grows; but, as they change, they approach or should approach more and more nearly to the perfect law. Modern science is built. upon the assumption that the relations between cause and effect are invariable, and that these relations may be grouped to form great natural laws, which express the modes by which the forces of the universe manifest themselves.

In this matter, science is frankly humble, and acknowledges that the region of the unknown is far greater than that of the known. Forces, relations and laws may exist as yet unknown to the world of science, which, used by a human or superhuman being, might to all appearances change well-established relations of known forces. That would be a miracle; but a miracle simply means a phenomenon not understood, in its cause and effect relations. It must also be admitted that men possess no absolute certainty that though certain forces, brought into a certain conjunction a thousand times, have produced the same effect, they will continue to do Should a variation occur, however, that also must be ascribed

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*See Grammar of Science, Pearson, pp. 117 and 118.

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