to devise means of isolating and distinguishing them. It was not because those substances were inaccessible that they were not previously discovered (for men had lived through ages in the closest contact with them), but for want of scientific knowledge, and of suitable and sufficiently refined methods of manipulation. In other cases where such knowledge and refined methods were not necessary, as in distinguishing diamonds, gold, silver, and various other bodies, the discoveries were made so long ago, that the records of them, if there were any, are lost. The discovery of gold required far less knowledge and intelligence than that of the vastly more abundant substances oxygen and nitrogen, because it was a glittering solid, and its properties more conspicuous. Even at the present time all our methods and appliances are extremely crude, when compared with the minuteness and complexity of molecular phenomena to be discovered. The most important truths are usually the least obvious. Many of the greatest truths remaining unknown can probably be discovered only by means of exhaustive researches which disclose exceptional instances, or of extreme refinements in science, which will enable us to detect and examine excessively minute residuary quantities of forces and substances; and the probable reason why we have not yet been able to discover an experimental connection between gravity and the various physical forces, is because of the extreme feebleness of the former force in comparison with the strength of the latter. For equal masses of matter, the proportionate strength has been estimated to be a mere fraction of 1 to 1,000 millions.1

The extremely limited extent of our faculties also keeps us in ignorance of many things. There is good reason for

1 The Unseen Universe, 5th edit., p. 145.

IMPORTANT TRUTHS ARE OFTEN HIDDEN ONES.

25

supposing that what would be a deafening chorus of insectsounds exists around us on a summer's day, entirely unnoticed by us, because our ear has no power to perceive vibrations exceeding a certain degree of rapidity; or, more correctly speaking, below a certain degree of intensity. Conversely, our loudest sounds may be inaudible to the

refined ears of insects.

As we cannot create knowledge, we are obliged when forming conclusions to draw them from the knowledge we possess; and the amount of that knowledge (though always increasing) is limited. As wider experience also enables us to discover exceptional instances and residuary quantities; and these compel us to infer the existence of wider laws and principles in order to include and explain them, so is it likely, and indeed almost certain, that some of the greatest truths remain still unknown, and will be discovered. In this way some of the most important truths have remained for ages unapparent. For instance, all our experience of the effect of applying heat to liquids confirmed our belief that at a particular fixed and definite temperature, different for each separate liquid, every substance passed abruptly from the liquid to the vaporous state, until Sir J. Herschel suggested, and Dr. Andrews a few years ago proved, that under suitable conditions of temperature and pressure, substances passed by a gradual change from the liquid to the vaporous structure, through an intervening series of conditions in which they could not be properly called either liquids or vapours. It is evident therefore, that as the amount of our experience and knowledge is still comparatively small, other great truths may in a similar manner remain unknown. That which is beyond reason at present may not be so in the future; but it has now no place in science for want of a basis of verified truth.

One cause of our being probably ignorant, even at the present time, of some of the grandest truths of nature is deficiency of special knowledge and experience. At any time a single new instance or experiment may suggest to us an idea of the possible existence of the grandest truth, or confirm a previously conceived hypothesis of its being. For instance, the new experiments of Cagnaird de la Tour caused Sir J. Herschel to suggest the probable continuity of the liquid and vaporous states of matter.' Did we also now know the true numerical relations, in the form of what has been termed 'homologous series' and 'periodic functions,' subsisting amongst elementary substances, we might be led to discover the existence and properties of new elementary bodies. Attempts to discover such relations have often been made, and one by Mendlejeeff has recently been published 2 and verified by the discovery of gallium.

We are most of us much more apt to congratulate ourselves upon what we have accomplished than to contemplate and compare with it what remains to be done. Our knowledge is finite, but our ignorance is nearly infinite. Even Newton compared himself to a little child picking up pebbles on the sea-shore, whilst the great ocean of truth lay expanded before him. Of the ultimate nature of time and space we know absolutely nothing; and of the essential natures of matter and force also nothing is known. The deepest truths require still deeper truths to explain them. The amount of discovery in the future appears likely to be vastly greater than that of the past. The study of science discloses our ignorance of a multitude of points which we may fully expect yet to know.

1 Sir J. Herschel's Discourse on Natural Philosophy, 1850, p. 234. 2 See Chemical News, No. 839, Dec. 24, 1875.

ENDLESS NATURE OF SCIENTIFIC RESEARCH.

27

New knowledge is not like a cistern, soon emptied, but is a fountain of almost unlimited power and duration. The discovery of one truth leads to that of many more. One new fact leads to a hundred researches, and each research evolves a hundred new facts, and so on. Not a single science, even of the mathematical ones, is probably yet complete either in principles or details. There is not a single force, nor even a single substance, yet completely understood. The area of scientific discovery enlarges rapidly as we advance; every scientific truth now known yields many questions yet to be answered. To some of these questions it is possible to obtain answers at the present time, others can only be decided when other parts of science are more developed. All the different branches of knowledge must advance together. A geometric and mechanical basis of physical science cannot be constructed until we know the forms, sizes, and positions of the molecules of substances; and as the whole realm of attainable knowledge appears immensely great in comparison with the powers of the human mind, the unfolding of it will probably require an almost infinite amount of labour, and therefore a vast period of time.

During the prosecution of an original investigation, the area of question and discovery enlarges as we proceed, and the research in some cases develops into such complexity and magnitude, that solution of its questions appears for a time hopeless. Generally however, when that discouraging point is attained, the subject begins to clear, and by persistent research is gradually reduced to order, and is found to conform to a few general laws or principles. What is true in this respect of a single investigation has been largely found to be true of some of the simpler sciences; for instance, celestial mechanics; and will probably be also found to be equally true of the

entire domain of discoverable science, i.e. its complexity will increase until a maximum is attained, and then be gradually resolved into a simple yet complete system of laws and principles in a similar manner.

Another reason for concluding that the future of science is immense is because, in a very large proportion of new experiments, we are unable to predict the results successfully. Knowledge of principles and laws enables us to predict effects; and the extent to which we are unable to predict successfully indicates, in a rough sort of way, the proportionate amount of such principles and laws yet to be found. If we take 100 parts of a mixture to analyse, and can only find 90 of them, we conclude that our knowledge of one-tenth of the bodies present is very incomplete; and similarly, if in 100 proposed new experiments we can only predict successfully the result of 10, the knowledge necessary to enable us to predict successfully the remainder has yet to be obtained. In many cases, however, our predictions are true, although we are unable to verify them, and allowance must be made for this circumstance. This inability to predict successfully occurs to the greatest extent with the greatest discoveries, and was specially true of the discoveries of electro-magnetism, and the magnetic relation of light.

As the human mind has discovered the present stock of scientific truth, and is rapidly finding more-and we fully believe that what remains to be ascertained must be of essentially similar character-it is reasonable to suppose that in course of time a vast deal more will be found; but how far man, with his finite intellect, will in the future be able to explain the phenomena belonging to the various parts of the universe, and successfully predict effects, no one at present can even guess. It is, however, reasonable to suppose that as the whole of nature is systematically