DIA 



DIA 



briefly add, that the following general 

 principle governs the formation of all 

 dials. Take the words of that great lumi- 

 nary of mechanics, the late James Fergu- 

 son, F. R. S. 



"If the whole earth were transparent 

 and hollow, like a sphere of glass, and had 

 its equator divided into 24 equal parts, by 

 so many meridian semicircles, one of 

 them being the geographical meridian of 

 any given place, say London ; and if the 

 hours of XII. were marked on the equa- 

 tor, both on that meridian, and on its op- 

 posite one, and all the rest of the hours 

 on the rest of the meridians, those meri- 

 dians would be the hour-circles of Lon- 

 don : then if the sphere had an opaque 

 axis, terminating at its poles, the shadow 

 of that axis would fall upon every particu- 

 lar meridian and hour, when the sun 

 came to the plane of the opposite meri- 

 dian ; and would, consequently, shew the 

 time at London, and at all the other places 

 on the meridian of London." 



DIALECT, an appellation given to the 

 language of a province, in so far as it 

 differs from that of the whole kingdom. 

 The term, however, is more particularly 

 used in speaking of the ancient Greek, 

 whereof there were four dialects, the 

 Attic, Ionic, JEolic, and Doric, each of 

 which was a perfect language in its kind, 

 that took place in certain countries, and 

 had peculiar beauties. In Great Britain, 

 besides the grand diversity of English 

 and Scotch, almost every country has a 

 dialect of its own, all differing considera- 

 bly in pronunciation, accent, and tone, 

 although one and the same language. 



DIALIUM, in botany, a genus of the 

 Diandria Monogynia class and order. Es- 

 sential character: calyx none; corolla five- 

 petalled; stamina at the upper side of the 

 receptacle. There is but one species, 

 viz. D. indum, a tree with alternate pin- 

 nate leaves, having seven ovate oblong, 

 acuminate, petioled, even leaflets, a hand 

 in length. Flowers panicled, nodding. 

 Native of the East Indies. 



DIALECTICS.in the literary history of 

 the ancients, that branch of logics which 

 taught the rules and modes of reasoning. 



DIALING lines, or scales, are graduat- 

 ed lines placed on rulers, or the edge of 

 quadrants and other instruments, to ex- 

 pedite the construction of dials. They 

 are, 1. A scale of six hours, which is on- 

 ly a double tangent, or two lines of tan- 

 gents each of 45, set together in the 

 middle, and equal to the whole line -of 

 sines, with the declination set against the 

 meridian altitudes in the latitude of the 



place. 2. A line of latitude, which is fit- 

 ted to the hour-scale, and is made by this 

 canon. As the radius : to the chord of 

 90 : : so are the tangents of each respec- 

 tive degree of the line of latitudes : to 

 the tangent of other arcs. And then the 

 natural sines of these arcs are the num- 

 bers, which, taken from a diagonal scale 

 of equal parts, shall graduate the divi- 

 sions of the line of latitudes to any radius. 

 The lines of hours and latitudes are gene- 

 ral, for pricking down all dials with cen- 

 tres. See DIAL. 



The other scales are particular, and 

 give the several requisites for all upright 

 declining dials by inspection. They are, 

 1. A line of chords. 2. A line for the sub- 

 stile's distance from the meridian. 3. A 

 line for the stile's height. 4. A line of the 

 angle of 12 and 6. 5. A line of inclination 

 of meridians. 



DIALOGUE, in matters of literature, 

 a conversation between two or more 

 persons, either by writing, or by word of 

 mouth. 



DIALYSIS, in grammar, a mark or 

 character consisting of two paints, ", 

 plac'r.l over two vowels of a word, in or- 

 der to separate them, because otherwise 

 they would make a diphthong, as mosaic, 

 &c. 



DIAMETER, in geometry, a right line 

 passing through the centre of a circle, 

 and terminated at each side by the cir- 

 cumference thereof. The chief proper- 

 ties of the diameter are, that it divides 

 the circumference of a circle into two 

 equal parts : hence we have a method of 

 describing a semicircle upon any line, as- 

 suming its middle point for the centre. 

 The diameter is the greatest of all chords. 

 For finding the ratio of the diameter to 

 the circumference, see CIRCLE. 



DIAMETER of a come section, or trans- 

 verse diameter, is a right line passing 

 through the centre of the section, or the 

 middle of the axis. The diameter bisects 

 all ordinates, or lines drawn parallel to 

 the tangent at its vertex. See Cosic 

 SECTIOMS. 



DIAMETER, conjugate, is a diameter, 

 in conic sections, parallel to the ordinates 

 of another diameter, called the transverse, 

 or parallel to the tangent at the vertex of 

 this other. 



DIAMETER, of any curve, is a right line, 

 which divides two other parallel right 

 lines in such manner, that, in each of 

 them, all the segments or ordinates on 

 one side, between the diameter and dif- 

 ferent points of the curve, are equal to 



