treats as a fact—viz., whether a given person is or is not angry, or intoxicated, or irrational—the witness is really testifying to the result, in his own mind, of his observations of the condition and conduct of the person who is under investigation, when compared with a standard which the witness has erected for himself. Hence such results are really matters of opinion evidence, pure and simple. Other examples of a like character are found in statements as to weight, height, distance, speed, and the like, as to which men of common powers of observation, who are not strictly experts, are, because of convenience and necessity and the probability of reasonable and ordinary accuracy, commonly permitted to give their own judgment and conclusions as evidence. _All Witnesses Often Permitted to Draw and State Conclusions in Matters involving Numerous and Complicated Details._—Thus the practical necessity of the administration of justice has led to the establishment of the rule, that where the details of an occurrence are numerous and complicated, and are incapable of precise description by ordinary observers, witnesses are permitted to use, in testifying, general expressions which really embody their conclusions from the facts or details observed by them. Greenleaf on Evidence, Section 440, note A; Wharton on Evidence, Section 434. Wharton says that “the distinction between expert witnesses and ordinary witnesses is this: the non-expert witness testifies to conclusions which may be verified by the adjudicating tribunal; the expert, to conclusions which cannot be so verified. The non-expert gives the results of a process of reasoning familiar to every-day life; the expert gives the results of a process of reasoning which can be determined only by special scientists.” See also People _v._ Fernandez, 35 N.Y., 49. People _v._ Deacons, 109 N.Y., 374-382. This learned writer (Wharton) also says, at Section 437 of the same treatise: “Where conclusions depend upon facts whose evidential weight can only be determined by those familiar with a particular specialty, then these conclusions may be given by experts in such specialty.” Such also is the exact derivative meaning of the word expert, it being derived from the Latin word “_expertus_,” meaning, literally, “experienced,” and hence skilled by experience.