TRA 



TRI 



of Arthur's seat, near Edinburgh, is 

 composed of this rock. 



TRAPE'ZIUM irpaTre^tov, a little 

 table). A term applied to any quadri 

 lateral figure which is not a parallelo 

 gram ; it is therefore inapplicable to the 

 square, the oblong, the rhombus, and 

 the rhomboid. Some writers apply the 

 term trapezoid to a quadrilateral, which 

 has only two sides parallel; and trape- 

 zium to a quadrilateral having two sides 

 parallel and the other two equal, but not 

 parallel. It has been proposed that trape- 

 zium should be the general word for 

 plane quadrilateral figures, parallelo 

 grams included ; and that trapezoid 

 should denote a quadrilateral figure 

 whose sides are not in the same plane. 



TRASS. A deposit of volcanic ashes 

 and scoriae ejected from the Eifel volca- 

 noes, and accumulated in valleys and old 

 lakes under the influence of water. It 

 is equivalent, or nearly so, to the puz- 

 zolana of the Neapolitans. 



TRAUBEN-ERTZ. The massive bo- 

 tryoidal variety of green lead ore, one of 

 the divisions of phosphate of lead or 

 pyromorphite. 



TRAUMATE. The name given by 

 the French geologists to graywack6. 



TRAVERSE. Traverse-sailing, or the 

 working of a traverse, is the method of 

 calculating a ship's place after she has 

 made two or more short courses on dif- 

 ferent points of the compass. 



TRAVERSE TABLE. A table used 

 in traverse-sailing and for other pur- 

 poses. It is a neat trigonometrical 

 canon, as follows :— The angle a ship 

 makes with the meridian is the angle of 

 the course ; the distance run in that 

 course is the hypotenuse of a right-angled 

 triangle, and the sirte opposite to the 

 angle of the course is called the depar- 

 ture (from the meridian). The side ad- 

 jacent to the angle of the course is called 

 the difference of latitude (this being found 

 from it by reducing miles or leagues to 

 degrees). The traverse table is a table 

 of double entry, into which, going with 

 the angle of the course and the distance 

 run, wte find in two columns the cor- 

 responding departure, and length of the 

 side, called difference of latitude. — Pen. 

 Cycl. 



TRAVERTIN. The Italian term for 

 a white concretionary limestone, usually 

 hard and semi-crystalline, deposited from 

 the water of springs holding lime in solu- 

 tion. The term is not exactly equivalent 

 to tufa, which expresses the loose and 

 S43 



porous surface deposit from calcareous 

 springs, wbile travertin denotes the more 

 solid limestone, less frequently formed 

 in lakes and on hill sides. This stone 

 was called by the ancients Lapis Tibur- 

 tinus, being found in great quantity by 

 the river Anio, at Tibur, near Rome. 

 Some suppose travertin to be an abbrevia- 

 tion of trasteverino from transtiburtinus. 



TREBLE. In Music, the highest part 

 in a concerted piece. It is distinguished 

 into the first or highest, and the second 

 or low treble. Half-treble, or mezzo 

 soprano, is a high counter-tenor. 



TREMATO'DA {rphi^a, a hole). An 

 order of sterelminthans, a parenchy- 

 matous entozoa, furnished with organs 

 of imbibition and adhesion in the form 

 of suckers. 



TRE'MOLITE. A sub-species of 

 straight-edged augite, named from Val 

 Tremola, where, however, it is not found. 

 It is distinguished into the asbestous, 

 the common, and the glassy varieties. 



TRIAD, HARMONIC. In Music, a 

 combination of three sounds which is 

 naturally divisible into two-thirds, one 

 major, the other minor, constituting a 

 fifth in the whole. Its name is derived 

 from its being formed of a third and a 

 fifth, which, with the base or funda- 

 mental sound, make three different 

 terms. 



TRIADE'LPHOUS (rpetr, three, idcX- 

 (pia, brotherhood). A term applied in 

 Botany to the filaments of plants which 

 are combined into three masses, or bro- 

 therhoods, as in some species of hype- 

 ricum. See Adelphia. 



TRIAKE'NIUM. The botanical de- 

 signation of a fruit which consists of 

 three achaenia, or cells. See Achcenium. 



TRIA'NDRIA (xpelf, three, itvrjp, a 

 man). The third class of plants in the 

 system of Linnaeus, comprising those 

 which have three stamens. 



TRI'ANGLE {tres angulos habens). A 

 three-sided figure, having necessarily 

 three comers or angles. When the lines 

 forming the sides are straight, the figure, 

 being on a plane, is called a plane tri- 

 angle : when they are curved, lying on 

 the surface of a sphere, the figure is a 

 spherical triangle. A triangle is equi- 

 lateral, when its three sides are equal ; 

 isosceles, when only two sides are equal ; 

 scalene, when all its sides are unequal ; 

 right-angled, when it has a right angle ; 

 obtuse-angled, when it has an obtuse 

 angle ; acute-angled, when it has three 

 acute angles. 



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