DI A 



DI A 



needle is less in proportion to the low 

 conducting power of the interposed sub- 

 stance. 



DIA'GONAL {dia, through, yavia, an 

 angle). A right line drawn across a 

 quadrilateral figure, from one angle to 

 another; by some called the diameter 

 of the figure. 



DI'AGRAM {dtdypafjifxa, a figure or 

 plan). A mathematical figure of any 

 kind, drawn for the purpose of illustra- 

 tion. 



DIAKE'NIUM. The term by which 

 Richard designates the fruit of the Um- 

 belliferae, from its consisting of two ake- 

 nia. See Achcenium. 



DIAL, or SUN-DIAL. An instrument 

 for determining the hour of the day by 

 the shadow of a point or line upon a 

 graduated surface. 



DI'ALECT (dmXcKTOp, discourse). The 

 language of a country, especially that of 

 a particular district; any variety of a 

 common language. 



DIALECTICS (3ia\e)CTtK6f, skilled in 

 argument). In Aristotle, this term de- 

 notes the logic of probabilities, as op- 

 posed to strict philosophical argument. 

 Plato employed it as synonymous with 

 metaphysics, or the highest philosophy. 

 The term simply means " the art of con- 

 versation," but is now generally applied 

 to the practical part of logic. 



DIA'LLAGE' (6ta\Xa7^, difference). 

 A variety of augite, generally of a bronze 

 yellow colour, possessing the most perfect 

 cleavage in the direction of the diagonal 

 of the prism, its natural joints and frac- 

 tures exhibiting a very different lustre 

 and appearance. 



Diallage Rock, or Euphotide. An orna- 

 mental stone, consisting of felspar and 

 diallage, in crystals aggregated together 

 in the manner of granite. The diallage 

 in the rock is called gabbro. 



DIALU'RIC ACID {bia, through, 

 oipovt urine). A new acid produced, in 

 combination with ammonia, by the de- 

 composition of alloxan tin. 



DIA'METER {hianerpeoa, to measure 

 through). A straight line passing through 

 the centre of a circle, and terminating 

 at both ends in the circumference. 



Diameter, transverse and conjugate. 

 These terms are applied to the two un- 

 equal diameters of an ellipse, the former 

 to the longer, the latter to the shorter, 

 diameter. They are also termed the 

 greater and the lesser axis. These lines 

 are at right angles to each other. Any 

 other line which passes through the cen- 

 106 



tre of an ellipse, and terminates in opp o- 

 site points of its circumference, is also 

 said to be a diameter. 



DIAMOND. A brilliant gem, consist- 

 ing of carbon in its highest state of 

 purity. Rose-diamonds are usually cut 

 out of the octohedral crystals ; brilliants, 

 from those with curvilinear faces. 



DIA'NDRIA (3if, twice, ixvt^p, a man ). 

 The second class of plants in the system 

 of Linnaeus, characterized by the presence 

 of two stamens. 



DIAPA'SON {bta iraawv, through all). 

 In Music, the interval of the octave ; the 

 compass of an instrument or of the 

 voice, a term signifying the same as con- 

 cert-pitch. 



DIA'PHANOUS {8ta, through, (paiva, 

 to show). That quality of a substance 

 which renders it permeable to light. 

 Translucent is a more common term of 

 the same import. Transparent expresses 

 more than translucent, implying not 

 merely the admission of light through 

 the substance, but the vision of external 

 objects. The terms semi-translucent and 

 semi-transparent denote feebler degrees 

 of these qualities. 



DIAPHO'NICS {&i<i, through, <p<avi], 

 sound). The doctrine of refracted sound. 

 DI'ASPORE (dtacTTopa, dispersion). 

 A rare mineral, which crackles by the 

 heat of a candle, and is dispersed in mi- 

 nute fragments. 



DI'ASTASE {6id<TTaais:, separation). 

 A vegetable principle, allied in its general 

 properties to gluten, which appears in the 

 germination of barley and of the seed of 

 plants, and converts their starch into 

 gum and sugar for the nutrition of the 

 embryo. The name is derived from its 

 property of separating two supposed con- 

 stituents of starch. 



DIATHE'RMANOUS (3m0ep/Liat'vco, to 

 warm through). A Greek term syno- 

 nymous with the Latin transcalent, and 

 denoting the free permeability of a sub- 

 stance by heat. 



Diathermancy. The property possessed 

 by nearly all diathermanous bodies, of 

 admitting the passage only of certain spe- 

 cies of calorific rays. When the quan- 

 tity of heat transmitted independently of 

 the quality is to be denoted, the term 

 diathermaneity has been suggested by 

 Melloni, in order to preserve the same 

 termination as in the word diaphaneity, 

 indicating the analogous property in re- 

 lation to light. 



DIATO'NIC SCALE {bid, through, 

 TOfor, a tone). A scale of music, con- 



