Page:Collier's New Encyclopedia v. 09.djvu/572

TRIANGLE OF FORCES 502 TRIASSIC SYSTEM TRIANGLE OF FORCES, in mechan- ics, a term applied to that proposition which asserts that if three forces, rep- resented in niap:nitude and direction by the sides of a triangle taken in order, act on a point, they will be in equilibrium; and conversely, if three forces acting on ft point, and in equilibrium, be repre- sented in direction by the sides of a tri- angle taken in order, they will also be represented in magnitude by the sides of that triangle. TRIANGLE OF HESSELBACH, in an- atomy, a triangular interval at the part of the abdominal wall through which the direct inguinal hernia passes. TRIANGLE OF SCARPA, in a n a t- omy, a triangu!-ar depression between the muscles covering the outer side of the femur and the adductor muscles on the inner side. It affords a passage for the femoral artery. TRIANGULUM, in astronomy, the triangle; one of the 48 ancient constella- tions. It is of small size, and is situated S. E. of Andromeda, N. of Aries, and W. of Perseus. The largest star, Alpha Tri- anguli, is only of the third magnitude. TRIANGULUM AUSTRALE, in as- tronomy, the Southern Triangle; a S. constellation of small size, but having the three stars which define it so promi- nent that they are sometimes called the triangle stars. The constellation is be- tween Pavo and Centaurus. TRIANGULUM MINUS, in astron- omy, the Lesser Triangle; an obsolete constellation of smaH size between Tri- angulum and Aries. It was established by Hevelius. TRIANOSPERMA, in botany, a genus of Cucurhitex, akin to Bryonia, but hav- ing only three seeds. They are climbing plants, with tendrils and monoecious flow- ers. Stamens three, ovary three-celled. Fruit globular, fleshy. Natives of the West Indies and Brazil. T. ficifolia, called also B. ficifolia, is an active purga- tive, and said to be a purifier of the blood. T. tayuya is given in Brazil in small doses as an emetic and in large ones as a purgative. TRIANTHEMA. in botany, a genus of Sesuvex. Sepals oblong, colored on the inside; stamens 5 to 12; styles one or two, filiform; capsule, oblong, trun- cate, circumscissile. Weeds from the tropical parts of both hemispheres and the sub-tropics of Africa. T. crystulliiui, T. monogyna {T. obcordata of Rox- burgh),^ T. pentandra, and T. decandra, are natives of India. The tender leaves and the tops of the second and third species are eaten by the natives; the seeds of the first also serve as food dur- ing famine. T. pentandra is used as an astringent in abdominal diseases, and is said to produce abortion. The roots of T. decandra and T. monogyna, the latter combined with ginger, are given as ca- thartics. TRIASSIC SYSTEM. This forms the basement group of the Mesozoic or Sec- ondary strata, and was formerly asso- ciated with the Permian system under the name of the New Red Sandstone. The term trias has reference to the three- fold grouping of the system in Germany, where the strata are more fully devel- oped than in Great Britain. In our area the system rests unconformably on the upturned and denuded edges of the Per- mian and older Palaeozoic strata. It is well developed in the central plains of England, whence a long belt extends N. from Nottingham to the valley of the Tees, while another band stretches down the Severn valley into Devonshire. Small areas likewise occur in Dumfriesshire and near Elgin, and also in the N. of Ireland. The system, however, assumes more importance in Central Europe, where it occurs at the surface over a wide tract between the Thiiringerwald in the E. and the Vosges Mountains in the W., and between Basel in the S. and Hanover in the N. N. of that region it continues underneath overlying forma- tions, but appears again and again at the surface where these latter are want- ing. Trias is also met vnith in Heligo- land and the S. of Sweden. In all the regions now noted the strata appear to have been deposited in inland seas. In the Alpine regions the Trias differs much from that of England and Ger- many. It attains a thickness of many thousand feet, and forms ranges of mountains. The lower division consists chiefly of fossiliferous limestones, the middle of shales, marls, limestones, and dolomites, while the Rhsetic is built up mainly of limestones and dolomites. Thus in Northwestern and Central Europe we have one well-defined type consist- ing of strata which have accumulated for the most part in inland seas, while in the Alpine regions the character of the beds betokens more open water. In France isolated areas of ^ Trias occur, some of which approximate in appearance to those of England, while others re- semble those of Germany. In Spain and Portugal both the German and Alpine types are represented. In North America the Trias is well de- veloped, as in Nova Scotia, Prince Ed-