EXPERT. 372 EXPLOSIVES. When his opinion is called for, it is ordinarily based upon a hypothetical question — that is, a question which supposes the statements of fact contained in it to have been established by com- petent evidence. Assuming the facts to be as stated in the question, the expert is asked to tell the jury what, in his opinion, is the correct in- ference to be drawn from them. It will be ob- served, therefore, that he is not asked to invade the province of the jury and decide the general question at issue, but only to testify to the specific inference that should be drawn from particular facts. Whether a person can be compelled to attend and testify as an expert for the fees of an ordi- nary witness is a question upon which the au- thorities are conflicting. In England and in many of our States it has been aswered in the negative, cither by judicial decision or by statute. This view is based upon two considerations: First, that to compel a person to attend as a witness merely because he is accomplished in a particu- lar science, art, or profession would subject the same individual to be called upon in every cause where his opinion would carry weight. Second, that a person's special knowledge and skill are property, which should be no more at the mercy of the public than the goods of the merchant, or the crops of the farmer. On the other hand, the view is maintained that the law allows no excuse for withholding evidence, and that the expert wit- ness, in the performance of his duty as a good citizen, should be compelled to testify where his evidence would be helpful to a court or jury, whether that evidence be based upon personal observation of some fact connected with the case, or upon his accumulated knowledge and experi- ence. It is generally agreed, however, that an expert cannot be required to make any special preparation or investigation for the opinion he is supposed to give, without extra compensation. The usefulness of expert evidence, and the ad- visability of changing the present methods of pro- curing and presenting it, are also questions upon which widely different views are entertained. A recent writer upon this subject, a lawyer of high reputation and sound judgment, has declared that "few judges have a good word to say for ex- pert testimony." Lord Campbell once told the House of Lords that expert witnesses "come with a bia- on their minds to support the cause in which they are embarked, and hardly any weight should be given to their evidence." Quite recently a learned judge in eu York City advised the jury "to put all the expert testimony out of their minds, and pay no attention to it," This he did although a week had been consumed in taking the expert testimony, because "an equal number oi doctors has testified directlj opposite to each other, and all with equal positiveness." On the i hand, the present system has its strong 1 no radical change is to be ex I in the near future. Consult : R :i - haw timony I Saint Louis, 1891) ; Law I . i ' and Opinion Evidt nci (2d ed., ' I! : Poster, "Expert Testimony, 1 iomplo ints, and Proposed Remedies" I I I Harvard I i ii w, 169) ; Endlich, "Pro po • in the Law of I • pert Testimony" <■'<-' il). See K [dence. EXPIATION, Day op. See Atonement, Day EXPLANATION ( Lat. explanatio, from ex- planar e, to explain, from ex, out -+- planare, to level, from planus, plain). In science, the giving of a complete description of some object or event. In certain cases this end is attained by the sub- sumption of the phenomenon to a general law, as when a physical fact is brought under one or other of the general laws of mechanics. The law, in such instances, is mathematically exact; it sums up in shorthand all the conditions under which the phenomenon in question appears; it sets the phenomenon in its right place within the causal nexus of the material universe. In fields of science that are less 'exact' than physics, such as biology and psychology, explanation takes on a different form. The laws of these sciences are, for the most part, hypothetical generalizations or supplementings of the facts more or less hypothet- ical in character, rather than shorthand formula derived from the facts themselves; so that sub- sumption to them, while it may help to confirm a theory or to classify an otherwise hetero- geneous subject-matter, does not constitute ex- planation. Nothing is more erroneous than the popular belief that a given fact is adequately explained when it is referred to a 'principle' of heredity or of memory. Explanation consists rather in an accurate description of the fact as observed, together with a statement, as full as the circumstances permit, of the proximate con- ditions under which it appears. Thus a fact of mind, a complex mental process, is explained when we have ( 1 ) analyzed it into its elements, sensation and affection, and (2) referred these constituent processes to their proximate physical conditions in the cerebral cortex. To explain, e.g. an impulse as a 'manifestation of our active nature' or of a 'faculty of will'; or to account for the rise of an idea in consciousness by a 'law of telepathy,' is to interpret a fact, a scientific datum, which can be known, in terms of the less known and hypothetical. Misunderstand- ings of this sort have recently called forth emphatic protest from men of eminence in scien- tific inquiry. 'The business of all science is the description of facts'; and when a scientific 'theory' goes beyond the specification of the conditions under which the facts are observable, it ceases to be an aid to thought and become positive hindrance. Consult: Kiilpe. Outlines of Psychology (Eng. trans. London, 1895) ; id., Introduction to Philosophy (Eng. trans. New York. 1897) : Mach. Contributions to the Analy- sis of the Sensations (Eng. trans. Chicago, 1897) ; Popular Scientific Lectures (Eng. trans. Chicago, 1895). EXPLOITS RIVER. A large river in New- foundland, rising in the southwest part of the island, which it almost Insects (Map: Newfound- land, E t). It takes a northeasterly course through the extensive Red Indian Lake and flows into the Bay of Exploits on the northeast coast. The fertile but sparsely sell led valley abounds with game, and the river with lish. it is navi- gable for i miles from its mouth by steamers. and small boats ascend within 50 miles of the Bouthwesf coast. EXPLOSION. Sec BALLISTICS. EXPLOSIVES (from Lat. cxplosus, p.p. of explodere, to explode, from ex, out + plaudere, to clap). Substances, either solid or liquid, which, under the influence of some disturbing agency,
