CHAPTER XXIX.
EXCEPTIONAL PHENOMENA.
If science consists in the detection of identity and the recognition of uniformity existing in many objects, it follows that the progress of science depends upon the study of exceptional phenomena. Such new phenomena are the raw material upon which we exert our faculties of observation and reasoning, in order to reduce the new facts beneath the sway of the laws of nature, either those laws already well known, or those to be discovered. Not only are strange and inexplicable facts those which are on the whole most likely to lead us to some novel and important discovery, but they are also best fitted to arouse our attention. So long as events happen in accordance with our anticipations, and the routine of every-day observation is unvaried, there is nothing to impress upon the mind the smallness of its knowledge, and the depth of mystery, which may be hidden in the commonest sights and objects. In early times the myriads of stars which remained in apparently fixed relative positions upon the heavenly sphere, received less notice from astronomers than those few planets whose wandering and inexplicable motions formed a riddle. Hipparchus was induced to prepare the first catalogue of stars, because a single new star had been added to those nightly visible; and in the middle ages two brilliant but temporary stars caused more popular interest in astronomy than any other events, and to one of them we owe all the observations of Tycho Brahe, the mediæval Hipparchus.
In other sciences, as well as in that of the heavens, exceptional events are commonly the points from which we start to explore new regions of knowledge. It has been beautifully said that Wonder is the daughter of Ignorance, but the mother of Invention; and though the most familiar and slight events, if fully examined, will afford endless food for wonder and for wisdom, yet it is the few peculiar and unlooked-for events which most often lead to a course of discovery. It is true, indeed, that it requires much philosophy to observe things which are too near to us.
The high scientific importance attaching, then, to exceptions, renders it desirable that we should carefully consider the various modes in which an exception may be disposed of; while some new facts will be found to confirm the very laws to which they seem at first sight clearly opposed, others will cause us to limit the generality of our previous statements. In some cases the exception may be proved to be no exception; occasionally it will prove fatal to our previous most confident speculations; and there are some new phenomena which, without really destroying any of our former theories, open to us wholly new fields of scientific investigation. The study of this subject is especially interesting and important, because, as I have before said (p. [587]), no important theory can be built up complete and perfect all at once. When unexplained phenomena present themselves as objections to the theory, it will often demand the utmost judgment and sagacity to assign to them their proper place and force. The acceptance or rejection of a theory will depend upon discriminating the one insuperable contradictory fact from many, which, however singular and inexplicable at first sight, may afterwards be shown to be results of different causes, or possibly the most striking results of the very law with which they stand in apparent conflict.
I can enumerate at least eight classes or kinds of exceptional phenomena, to one or other of which any supposed exception to the known laws of nature can usually be referred; they may be briefly described as below, and will be sufficiently illustrated in the succeeding sections.
(1) Imaginary, or false exceptions, that is, facts, objects, or events which are not really what they are supposed to be.
(2) Apparent, but congruent exceptions, which, though apparently in conflict with a law of nature, are really in agreement with it.
(3) Singular exceptions, which really agree with a law of nature, but exhibit remarkable and unique results of it.
(4) Divergent exceptions, which really proceed from the ordinary action of known processes of nature, but which are excessive in amount or monstrous in character.
(5) Accidental exceptions, arising from the interference of some entirely distinct but known law of nature.