TOP 



TOP 



fcag not fo rich and fine a colour as the former. The Saxon 

 topaz is diftinguilhed by its wine-yellow colour, and when 

 cut, often exhibits a luftre equal to that of the fineft oriental 

 varieties. The mountain-green varieties of topaz, which 

 are found in Siberia, are included under the name of aqua 

 marine. The Brafilian ruby and fapphire include the red 

 and blue Brafihan topaz. 



The topaz may generally be diftinguiihed from all other 

 minerals by the vhomboidal bafe of its cryllals, the frafture, 

 and crofs lamellar ftrufture, and by the longitudinal ilreaks 

 on its fide planes. It is lefs hard and heavy than yellow 

 fapphire, and the latter does not become eledric by lieating. 

 The fame charafters diftinguifh it from fpinel : it is further 

 diftinguiihed from fpinel by its double refraftion. Green- 

 coloured topaz is diftinguifhed from beryl by its greater 

 fpecific gravity, that of topaz being 3.5, and of beryl only 

 2.7. Ttie latter cleaves in the direftion of its lateral planes, 

 which the topaz does not. 



The following minerals have been denominated topazes, 

 when colour was confidered as affording the moft certain 

 charafter of precious ftones. 

 I. Yellowifh- white fap- ^ 

 phire 



2. Zircon 



Chryfolite 

 Yellowifh beryl 



Yellow rock-cry llal 



Clove-brown and brown 

 rock-cryftal 



> 



■^ "i 



Oriental topaz. 



Hyaline and yelloui(h-red 



topaz. 

 Yellowifh -green topaz. 

 Siberian topaz. 

 Bohemian or Occidental 



topaz. 



Smoke topaz. 



Names gi\en to varieties of the topaz. 



Aqua marme. 



Sapphire. 



Chryfoprafe. 



Rubicele. 



Brafilian or Balais ruby., 

 Saxon chrvfolite. 



I. Mountain green topaz 



I. Blue topaz 



3. Yellow topaz 



4. Wine-yellow inclining f =3 ■ 



to red topaz 



5. Red topaz 



6. Yellowifh-green topaz 



See Sapphire, Ruby, and Gems. 



A peculiar property of the topaz was difcovered by Vau- 

 quehn, that the powder of this gem changes the fyrup of 

 violets to green if it remain in the liquor two or three hours, 

 and this property is common to all the varieties of the 

 topaz. 



Mr. Canton, in 1 760, found that the Brazil topaz has the 

 eleflrical properties of the tourmahn. 



Tiie topaz is eafily counterfeited ; and there are faftitious 

 ones, which, to the eye, are not inferior to the natural 

 ones. 



To counterfeit the topaz in glafs, fee Glass refemlling 

 Topa%. 



To counterfeit the oriental topaz in parte : Take cryftal 

 prepared, two ounces ; ordinary minium, or red lead, feven 

 ounces : put thefe into a crucible luted, and bake them 

 twenty-four hours in a potter's kiln. If the mafs is not 

 fufficiently clear and fine, cover it up again, and give a 

 fecond baking, and it will come out of a fine topaz colour. 

 See Paste. 



If we might believe the ancients, the topaz has very not- 

 able virtues ; but thofe are now in difcredit. See Gem. 



TOPAZOS, or Topazius, in Ancient Geography, an 

 idand placed by Pliny in the Red fea, 300 ftadia from the 

 continent. 



TOPDALS, in Geography, a town of Norway, in the 

 province of Chriftianfand ; 32 miles N. of Chriftianfand. 



TOPE, in Ichthyology, an Englifli name for a fpecies of 

 the fqualus, according to the Artedian fyftem, the fqualus 

 galeus of Linnssus, diftinguifhed from the other fquah by 

 the noftrils being placed extremely near the mouth, and by 

 certain foramina, or apertures, near the eyes. It is the fi(h 

 called by the ancients y«?,so; wm, galeus cams and caniculata. 

 See Squalus. 



TOPEL, or Tapi., in Geography, a town of Bohemia, 

 in the circle of Pilfen ; 56 miles W. of Prague. . N. lat. 

 49'^ 58'. E. long. 12° 57'.. — Alfo, a river of Bohemia, 

 which runs into the Egra, near Carlfbad. 



TOPERS Hat, a fmall ifland in a bay on the N. coafl 

 of New Guinea. S. lat. 3° 5'. E. long. 135° 33'. 



TOPETINA, a town of Mexico, in the province of 

 Mechoacan, at the mouth of a river near the Pacific ocean ; 

 50 miles N.W. of Zacatula. N. lat. 18° 56'. W. long. 



103° 44'- 



TOPETRY, a town of Hiudooftan, in the Carnatic ; 

 50 miles S.E. of Tanjore. 



TOPHATH, in Ancient Geography, a place in the Land 

 of Paradife, near the Dead fea. Jofiah deftroyed this place 

 on the abolition of idolatry. 



TOPHUS, a kind of node, or fwelling of the periof- 

 teum. Alfo, the fort of concretion found in the joints o? 

 gouty perfons. 



Tophus, in Natural Hi/lory, is a fpecies of fand-ftone, 

 called alfo poms, moftly of a grey colour ; but it is alfo 

 found of other colours, as whitifh, brownifh, &c. accord- 

 ing to the foil in which it is imbedded. It much refembles 

 the pumice in texture, being rough and brittle, and com- 

 pofed of a large angular grit, cemented by a very coarfe 

 terrene cryllalline fubilance. It is too foft to llrike fire 

 with fteel. It is common in Italy and in Germany, where 

 it is ufed for building, chiefly for cellars and turning arches. 

 DaCofta's Hift. FofTils, p. 136. 



TOPI, in Geography, a fmall ifland in the Mediterranean, 

 near the N. coaft of the ifland of Elba. N. lat. 42° 51'. 

 E. long. 1 1° 30'. 



TOPI A, a town of Mexico, in the province of Culiacan ; 

 80 miles N. of Culiacan. N. lat. 25° 44'. W. long. 108°. 



TopiA, the chief chain of mountains in Spanifh North 

 America, commencing in the neighboiu-hood of Guadalax- 

 ara, and extending north to New Mexico, a diilance of 

 150 leagues, or, according to our maps, more than 700 

 Britiih miles ; while the breadth of all the ridges is, accord- 

 ing to Alcedo, fometimes' 40 leagues, or 160 miles. This 

 chain is of fuch a height as to be comparable with the 

 Andes of Peru, and abounds with precipices of the moft 

 profound and terrible afpecl. It is almoft univerfally denfely 

 clothed with large and lofty pines, and other trees which af- 

 ford fuftenance to birds of very variegated and beautiful ap- 

 pearance. On the fummit the cold is intenfe, but the tem- 

 perature on the fides varies according to climate and ex- 

 pofure. It is the fource of many rivers flowing into the 

 Atlantic and Pacific, and fubjcck, on the melting of the 

 fnow, to very confiderable inundations. During the rains, 

 which laft from June to September, the rivers become ter- 

 rible in their devaflations to the diftance of two or three 

 leagues, and the mofquitoes become intolerable. Among 

 the animals in thefe regions, are bears, lions, and tigers, as 

 well as fquirrels of various kinds. This chain is prohfic in 

 filver, yielding about a mark for each quintal of earth. It 

 received its name from a favage tribe, which was converted 

 by the Jefuits in 1590 ; but the mines, on account of their 

 diftance from the capital, have been moftly abandoned. The 

 ridge of Topia is alfo called the " Sierra Madre," or mother- 

 chain, and embraces the fingulai- province of Nayarit, which 

 6 remained 



