TAN 



31 



TAN 



make a tangent plane horizontal, there is absolutely no 

 descent in one direction, or, by going along the tangent 

 plane, we can remain entirely on the surface, in one cer- 

 tain direction, as before observed. And the direction ol 

 most rapid descent is at right angles to this direction ol 

 no descent. 



To put a case of the third kind, suppose a saddle placed 

 on a horse, and we take the lowest point of the seat. The 

 tangent plane then cuts through the saddle horizontally. 

 In gome directions there is descent, in others ascent, with 

 two directions in which there is, comparatively speaking, 

 neither ascent nor descent. The direction of most rapid 

 "-(nit, which is from the lowest point of the seat directly 

 towards the head or tail of the animal, is at right angles 

 to the direction of most rapid descent. Mathematically 

 speaking, the curvatures of the vertical sections are some- 

 times positive, and sometimes negative, and the direction 

 of the greatest negative (or algebraically least) curvature 

 is at right angles to the direction of the greatest positive 

 i. or algebraically greatest) curvature. 



As to points connected with the apparent physical cha- 

 racter of the tangent, which have been in various places 

 referred to this article, it will be more convenient to con- 

 sider them under the word VELOCITY. 



TANGHI'.NIA. the name of a semis of plants belonging 

 to the natural order ApocynaeesD. This name was irivc.n 

 by Aubert du Petit Thmiars to the plant which produces 

 the celebrated Tanghin poison of Madagascar. The genus 

 possesses an int'undibulifbrm corolla, with a clavate tube, 

 and 5-tuothed throat : the anthers are subsessile : the fruit 

 is a drupe, with a fibrous ligneous putamen or stone, which 

 contains one or two seeds. The specific name T. veneni- 

 fera was given to the plant which yields the poison. It 

 has dense leaves, with erect branches, and pauiculated 

 terminal flowers. At the time Du Petit Thouars described 

 this plant, he stated that it was closely allied to theCerbera 

 Manghas ; and since its cultivation by Mr. Telfair in the 

 Mauritius, there can be no doubt of its belonging to the 

 genus Cerbera, and the plant is now called C. Tanghin. 

 native island this plant attains the size of a tree, and 

 has a hard wood which may be used for many kinds of 

 carpentry. But the part which yields the poison is the 

 kernel of the fruit. Although this kernel is small, not 

 much larger than an almond, Mr. Telfair says that it con- 

 tains enough poison to kill twenty persons. Its great use 

 in M .vas as a means of trial, the innocent being 



supposed able to resist its action, whilst the guilty suffered 

 under its influence. Radama, the late king of Madagascar, 

 was desirous of abolishing its use, but found great diffi- 

 culty in doing so on account of the prejudices of the na- 

 tucs. Mr. Telfair witnessed a sad instance of its use. 

 The king Hadania was taken ill, and got well by the use 

 of mercury ; but this medicine affected his mouth, so that 

 the impression produced upon his ' skid,' or physician, was 

 that the king hail been poisoned. He therefore in- 

 that the Tanghin should be administered to himself and 

 all the servants of the household, in order to ascertain the 

 guilty party. The king protested against the procedure, 

 but in vain. The whole household were shut up during 

 the night without food, and in the morning were brought 

 out for trial. The presiding ' skid,' or physician, then 

 pounded the Tanghin bean to a pulp between two stones, 

 and applied a small quantity to the back of the tongue of 

 each individual. The effects varied in different indivi- 

 duals, lu some it produced vomiting, and the poison be- 

 ing ejected from the stomach, they recovered. In other* 

 convulsions were brought on with violent efforts at vomit- 

 in?, which soon destroyed life. (Botanical Magazine, fol. 

 KiM. 



TAN'fUKK. [MAKOCCO.] 

 TANGLE. [SKA-WBKDS.] 



TAN'GUT is the historical name of a country in Asia, 



whid, the centre of the eastern, more extensive, 



and more elV% ated table-land of that continent [Asi.v, vol. 



ii.. p. -Kit 1. 1. 1 1 ere a nation, which originally inhabit cd Tibut, 



anil Tang, founded an empire in the seventh 



century, which was very powerful for a long time, and was 



his Khan in 1227. The country still 



me of Tangut, though at present a pail of 



it is i <l in the Chinese province of Kansi, whilst 



ily in possession of two Mongol nations, 



tip- ( (loth 'IVhi ii-os and the Torbod Mongols. 



i on China Proper on the north-west, ex- 

 i 33" and 42 N. lat., and between W and 



107 E. long. To the south of it is Tibet ; to the west Chi- 

 nese Turkistan, or the government of Thian-Shan Nanlu 

 and to the north Mongolia, of which also a portion is in- 

 cluded within the lately erected province of Kansi. As the 

 boundary-lines of the" country are not politically deter- 

 mined, it is not possible to give an estimate of the area. 



The southern portion of Tangut, or that which lies south 

 of 38 N. lat., is one of the most mountainous tracts on the 

 globe, and extends over the upper course of the river 

 Hoang-ho and the basin of the lake of Khookhoo-nor. 

 Along its southern border there is a very elevated range, 

 which divides the upper courses of the rivers Hoang-ho 

 and Yan-tse-kiang, and is called the Bayan Khara range. 

 [BAYAN KHARA MOUNTAINS.] Another elevated range 

 traverses the country in the same direction from cast to 

 west near 38 N. lat. This range rises at a short distance 

 from the banks of the Hoang-ho north of the town of Lan- 

 tcheou, and in its eastern part is called Kilian Shan ; but 

 farther west it takes the name of Nan Shan (or Southern 

 Chain). It rises to a great elevation, especially towards the 

 west, where manyof their summits are covered withsnowand 

 united by extensive glaciers. This mountain-chain is sup- 

 posed to be connected with the Kuenluen range near 92 E. 

 long. These two ranges above mentioned occupy a great 

 portion of the country between 33 and 38 N. lat.. and nearly 

 the whole of the remainder of the country is filled up by a 

 third range, which connects these two ranges, and extends 

 from south-east to north-west, being on the north united to 

 the Nan Shan, and on the south to the Bayan Khara Moun- 

 t kins. This chain bears the name of Sine Shan, or Snowy 

 range, on account of the numerous summits which rise, 

 above the snow-line. The river Hoang-ho breaks through 

 this range, but the huge rocky masses compel the river to 

 make a great bend towards the west between 34 and 30 

 N. lat., and the circuit which the river makes shows the 

 immense extent of these masses of rock. In this part of 

 its course the river is said to be hemmed in by lofty moun- 

 tains, so that no communication can be established along 

 the banks. Its course above this bend is very imper- 

 fectly known, and the fabulous accounts of its sources show 

 that they have never been visited even by Chinese geo- 

 graphers. The river enters a wide valley by n narrow 

 gorge formed by two very elevated mountains a little 

 above the town of Ho-cheou (36 J^. lat. and 102 E. 

 long.). At the opening of this gorge is a fortress, called 

 Tsy-shy-kuan. 



Tangut is separated from China Proper by a fourth 

 range, the mountains of Sifan, which run south and north, 

 being connected at their southern extremity with the 

 Bayan Khara Mountains and the Siue Shan by au exten- 

 sive mountain-knot, which is in the country formerly called 

 Sifan, whence the chain has obtained its name. Though 

 this range is less elevated than the Siue Shan, it rises in 

 several places above the snow-line, and occupies a con- 

 siderable width. It is supposed to terminate near the 

 banks of the Hoang-ho, a tew miles south of 38 N. lat. 

 Opposite to it and on the northern banks of the river rises 

 another chain, which may be considered as the continua- 

 tion of the mountains of Sifan ; but this range, which con- 

 tinues along the western bank of the river as far north as 

 42 N. lat., rises only to a moderate elevation, and is 

 stated to occupy in many places only three or four miles 

 in width : it is called Holang Shan, and slopes on the 

 west down into the steppe of the Oliith Tshoros. This 

 range is distinguished from all the other ranges of Tangut 

 by being thickly wooded on its eastern declivity. 



Only a small portion of the countries enclosed by these 

 mountain masses is fit for cultivation. It does not appeal- 

 that there is any cultivation in the upper valley of the 

 Hoang-ho above the fortress of Tsy-shy-kuan. Below that, 

 place and as far as Lan-tcheou, the valley is wider, and 

 narrow tracts along the banks of the river are cultivated 

 and fertile. This part of the valley is compared wilh that 

 of the Adige in Tyrol. Farther down, and as far as the 

 neighbourhood of Ning-hia, a town built on the western 

 janks of the Hoang-ho, at the eastern declivity of the Ho- 

 lang Shan (3H U 32' N. lat.), the valley has not been visited 

 jy Europeans. At this place the river runs in a wide \ alley 

 which has been rendered fertile by numerous canals, which 

 uc fed by the waters of the river, nnd in which lire, is ex- 

 tensively cultivated. There arc also numerous plantations 

 of fruit-trees. The soil contains much saltpetre. The town 

 of Ning-hia, the ant lent capital of Taugtit, is of consider- 

 able extent, being fifteen li (equal 1o five miles) in cir- 



