Diæ´resis, a separation of one syllable into two, also the mark (¨) by which this separation is distinguished, as in aërial.
Diagno´sis, in medicine, the recognition of diseases by their distinctive signs or symptoms; the discovery of the true nature and seat of a disease.
Diag´onal Scale, a scale which consists of a set of parallel lines drawn on a ruler, with lines crossing them at right angles and at equal distances. One of these equal divisions, namely, that at the extremity of the ruler, is subdivided into a number of equal parts, and lines are drawn through the points of division obliquely across the parallels. With the help of the compasses such a scale facilitates the laying down of lines of any required length to the 200th part of an inch. The length 1·67 inches, for example, is given by EF in the figure. Similarly AB = ·91 inch, CD = ·84 inch.
Diag´oras, ancient Greek poet and philosopher, born in Melos, an island of the Cyclades, and flourished about 425 B.C. He spent a great part of his life in Athens. Like his teacher, Democritus, he attacked the prevailing polytheism, and sought to substitute the active powers of nature for the divinities of the Greeks. On this account he had to leave Athens.
Di´agram (Gr. diagraphein, to describe), a figure or geometrical delineation applied to the illustration or solution of geometrical problems, or any illustrative figure in which outlines are chiefly presented, and the details more or less omitted.
Dial, or Sun-dial, an instrument for showing the hour of the day from the shadow thrown by a stile or gnomon upon a graduated surface while the sun is shining. This instrument was known from the earliest times amongst Egyptians, Chaldeans, and Hebrews. From those Eastern nations it came to the Greeks. It was introduced into Rome during the first Punic War. Dials are of various construction, horizontal, inclined, or upright, the principle in every case being to show the sun's distance from the meridian by means of the shadow cast by the stile or gnomon. The stile is made parallel with the earth's axis, and may be considered as coinciding with the axis of the sun's apparent diurnal motion. Consequently, as the sun moves westwards the shadow of the stile moves round opposite to it, in the same direction, falling successively on lines drawn to represent the hours of the day. The dial, of course, gives true solar or apparent time, which, except on four days of the year, is somewhat different from mean time. Dials are now rather articles of curiosity or ornament than of use.—Bibliography: Leybourn, The Art of Dialling; Dawbarn, The Sun-dial.
Di´alect, the language of a part of a country, or a distant colony, deviating either in its grammar, vocabulary, or pronunciation, from the language of that part of the common country whose idiom has been adopted as the literary language, and the medium of intercourse between well-educated people. Although the use of provincial dialects becomes inconvenient after a language has acquired a fixed literary standard, the study of such dialects is always valuable to the philologist for the light they throw on the history of the language. The diffusion of education and of printed books has much relaxed the hold which the provincial dialects of various countries once had on the people, and in general it may be said that the educated classes of any country now speak each of them a uniform language.
Dialec´tics (Gr. dialektice, from dialektos, discourse, dialogue), a philosophic term originally signifying investigation by dialogue. It was first