Given the results of observation or experiment, the philosopher endeavours to discover a law or principle connecting them. He guesses at their meaning, and invents a hypothesis which will not only explain what is known, but also suggest consequences which may, or may not, be confirmed by future investigations. Prof. A. Senier relates that von Hofmann used to say to him and other research students working in the Berlin laboratory, "I will listen to any suggested hypothesis, but on one condition-that you show me a method by which it can be tested." Without such a condition, the creations of a disordered mind would be as worthy of consideration as the speculations of a scientific genius; and fertile ideas would be sought not in a laboratory but in an asylum. A hypothesis ought, therefore, to be capable of being verified, even though the means may not be available of applying a crucial test to it at the time; it ought also to be sufficiently definite to admit of proof or condemnation.

Imagination as distinguished from fancy is an essential attribute of the scientific mind that makes for progress. "With accurate experiment and observation to work upon," says Tyndall, “imagination becomes the architect of physical theory. Newton's passage from a falling apple to a falling moon was an act of the prepared imagination. Out of the facts of chemistry the constructive imagination of Dalton formed the atomic theory. Davy was richly endowed with the imaginative faculty, while with Faraday its exercise was incessant, preceding, accompanying and guiding all his experiments. His strength and fertility as a discoverer are to be referred in great part to the stimulus of the imagination." Darwin was equal to Faraday in imaginative power; he was continually forming theories,

but his fertility in this respect was balanced by the power of severe criticism to which he subjected the products of his imagination. His son says that he was willing to test what would seem to most people not at all worth testing; and that he enjoyed making what he called "fools' experiments" to judge whether a view or hypothesis was false or true.

In science, however, the value of the imagination increases with breadth of knowledge. A child may imagine the stars to be windows in the vault of heaven, and their twinkling the fluttering of angels' wings passing in front of them. His conception of the stellar universe may be beautiful, but it differs widely from that on which the astronomer endeavours to construct a scientific cosmogony.

How easy it is to overlook objects and phenomena when their significance is not understood is illustrated by an incident related by Darwin himself. While a student at Cambridge, he went to Wales with Sedgwick, the professor of geology, and examined the rocks for fossils. This was before Agassiz had shown that at one period of geological history the rocks of the country must have been buried beneath a sheet of ice which left unmistakable marks of its action upon them. But," says Darwin, "neither of us saw a trace of the wonderful glacial phenomena all around us; we did not notice plainly scored rocks, the perched boulders, the lateral and terminal moraines. Yet these phenomena are so conspicuous that, as I declared in a paper published many years afterwards in the Philosophical Magazine, a house burnt down by fire did not tell its story more plainly than did this valley."

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Imaginative writers may produce fantastic romances in which future conditions are portrayed, but neither

they nor the prophet who bases his prediction upon existing knowledge can forecast with any confidence the character of new discoveries. It is often easy to foretell the development and further application of knowledge already acquired, but this system of extrapolation of curves of existing conditions cannot take into consideration the discovery of new factors which may alter, and frequently do alter, the trend of tendency. Even an author like Mr. H. G. Wells, with wide scientific learning upon which to build his brilliant romances, could not anticipate such discoveries as wireless telegraphy, Röntgen rays or radium, though he could foresee extensions of existing knowledge, and visualise social effects of progressive science and invention.

Science advances by opening completely new fields of knowledge upon which the literary man or investigator may exercise their intellectual activities, and the directions in which these domains are to be found are rarely indicated with success in romantic or in scientific literature. Because it is impossible to know what future work will bring forth, purely imaginative forecasts of things to come are probably as much, or as little, to be depended upon as strictly logical conclusions based upon accomplished fact. True it is that "whether there be prophecies, they shall fail; whether there be tongues, they shall cease; whether there be knowledge, it shall vanish away."

CHAPTER VII

LAW AND PRINCIPLE

The great tragedy of science the slaying of a beautiful hypothesis by an ugly fact. Huxley.

Consistency in regard to opinions is the slow poison of the intellectual life, the destroyer of its vividness and its energy. Sir Humphry Davy.

Of all monarchs Nature is the most just in enactment of laws, and the most rigorous in punishing the violation of them. Wilkins.

Though the mills of God grind slowly,

Yet they grind exceeding small:"
Though with patience he stands waiting,

With exactness, grinds he all. Longfellow. Nature is so varied in her manifestations and phenomena, and the difficulty of elucidating their causes is so great, that many must unite their knowledge and efforts in order to comprehend her and force her to reveal her laws. Laplace.

For Nature, Time is nothing. It is never a difficulty: she always has it at her disposal: and it is for her the means by which she has accomplished the greatest as well as the least results. Lamarck.

IN a scientific sense, a natural law is merely a precise statement of the relationship between certain results of observation. Facts must first be collected by observation or measurement; then they have to be classified and compared with the view of finding any relationship existing between them. When a relation is discovered

which shows the dependence of one group of facts upon another, it is called a scientific law, or a law of Nature. Often the law can be expressed in mathematical terms; but it may be only a brief description in words of certain relationships in the field of Nature. In either case, there must be no exception to the law. The laws of civil life can be broken, and sometimes are broken deliberately in order to direct attention to their injustice. But a law of Nature is simply a statement of relationship, and when observations prove the statement to be incorrect, then the law has to be abandoned or modified to take the new facts into consideration.

The method of science, indeed, is the method of the Chancery Court-it involves the collection of all available evidence and the subjection of all such evidence to the most searching examination and cross examination. False evidence may be tendered and for the time being accepted; but sooner or later the perjury is discovered. Our method, in fact, goes beyond that of the courts: we are not only always prepared to reconsider our judgments but always searching for fresh evidence; we dare to be positive only when, time after time, the facts appear to warrant a definite conclusion. Prof. H. E. Armstrong.

The broad generalisation which is accepted as a law of Nature by one generation may thus prove to be only an approximation to the truth when fuller knowledge has been acquired. When a formula expressing relationships between facts or phenomena in Nature is so exact and comprehensive that it suffices for whatever new knowledge has been gained by the increase of perceptive powers from one generation to another, it stands out as a great achievement of scientific thought.

The grand, and indeed only, character of truth is its capability of enduring the test of human experience, and coming unchanged out of every possible form of fair discussion. Sir John Herschel.

Pre-conceived ideas and traditional beliefs are drags