A Method of Expressing Ear-Power in Degrees of a Fixed Scale

Science becomes exact and trustworthy in proportion as it deals with number, measure and weight. Whatever is vague and ill-defined must be replaced by what is definite and numerical. Prescriptions, for instance, which used to order "a pinch" of one ingredient, "a little" of another, and " a good drop" of a third, are now given in drams and scruples. Visual capacity has for some years been gauged by accurate tests; and if the total visual power be defective, it can be so analysed as to localise the defect either in the horizontal plane, or in the vertical, or in some other direction. But the tests