803 
T O U 
fourth part of their breadth in thickness, and 
an inch and a half long ; these being thus pre- 
pared, you are to engrave on each a mark 
indicating its purity, or the nature and quan- 
tity of the. admixture in it. The black rough 
marbles, the basaltes, or other softer kinds of 
black pebbles, are the most proper for touch- 
stones. 
The method of using the needles and stone 
is this : The piece of metal to be tried, ought 
first to be wiped well with a clean towel, or 
piece of soft leather, that you may the better 
see its true colour ; for from this alone an 
experienced person will, in some degree, 
judge beforehand what the principal metal is, 
and how and with what debased. Then 
cliuse a convenient*, not overlarge, part of 
the surface of the metal, and rub it several 
times very hardly and strongly against the 
touchstone ; that in case a deceitful coat or 
crust should have been laid upon it, it may 
be worn off by that friction : this, however, 
is more readily done by a grindstone, or 
small tile, if you have them at hand. Then 
wipe a flat and very clean part of the touch- 
stone, and rub against it, over and over the 
surface of the piece of metal, till you 
.have, on the flat ' surface of the stone, a 
•thin metallic crust, an inch long, and about 
an eighth of an inch broad ; this done, look 
out the needle that seems most like tire 
metal under trial, wipe the lower part of this 
needle very clean, and then rub it against 
4he touchstone as you did the metal, by the 
side of the other line, and in a direction pa- 
rallel to it. When this is done, if you rind 
no difference between the colours of the two 
marks made by your needle and the metal 
under trial, you may, with great probability, 
pronounce that metal and your needle to be 
of the same alloy, which is immediately 
known by the mark engraved on your needle. 
But if you rind a difference between the co- 
-Tour of the mark given by the metal, and 
that by the needle you have tried, choose 
out another needle, either of a darker or light- 
er colour than the former, as the difference 
of the tinge on the touchstone directs ; and 
by one or more trials of this kind you will 
be able to determine which of your needles 
the metal answers, and thence what alloy it 
is of, by the mark of the needle ; or else 
you will find that the alloy is extraordinary, 
and not to be determined by the comparison 
of your needles. 
TOURMALINE, in mineralogy, a species 
of siliceous earth. It has been found only in 
Ceylon, Brazil, and Tyrol. That of Ceylon 
is of a dark-brown or yellowish colour ; its 
specific gravity 3.065, or 3.295 ; that of Bra- 
zil is green, blue, red, or yellow, and its spe- 
cific gravity 3.075 or 3. 180 ; that of Tyrol by 
reflected light is of a blackish brown, but by 
refracted light yellowish, or in thin pieces 
green ; its specific gravity 3.050 ; mostly cry- 
stallised in polygonal prisms, but sometimes 
amorphous. The thickest parts are opake ; 
the thin more or less transparent. See 
Shorl. 
TOU RNEFORTI A,a genus of the pen- 
tandria monogynia class of plants, the 
flower of which consists of a single petal, 
in form of an oval tube, longer than the 
calyx, divided into five slight segments some- 
what broad and pointed, and spread open ; 
the fruit is a globose berry, containing two 
T ft A 
1 cells : and the seeds are of an oval figure, 
two in number, and separated by the pulp. 
There are eleven species, shrubs of South 
1 America. 
| TOURNEQUET. See Surgery. 
j TOU RRE IT! A, a genus of the didynamia 
j angiospermia class and order. The cal. is 
| two-lipped ; cor. lower lip none ; caps, echi- 
' nate, four-celled, two-valved. There is one 
species, an annual of Peru. 
TOWER, any high building raised above 
another, consisting of several stories, usually 
ot a round form, though sometimes square or 
polygonal ; a fortress, a citadel. Towers are 
built for fortresses, prisons, &c. as the tower 
ot the Bastile, which was destroyed by the 
inhabitants of Paris in 1789. 
The tower, of London, commonly called 
The Tower, is a building with live small 
turrets at different angles above it, situated 
ori the banks of the river Thames. The 
guards usually do duty in it. It is at present 
garrisoned by the invalids. The tower of 
London is not only a citadel to defend and 
command the city, river, &c. but it is also 
a royal palace, where the kings of England 
with their courts have sometimes lodged ; a 
royal arsenal, wherein are stored arms and 
ammunition tor sixty thousand soldiers ; a 
treasury for the jewels and ornaments of the 
crown ; a mint for coining money ; the ar- 
chives wherein are preserved all the antient 
records of the courts of Westpii aster, &c. 
and the chief prison for state delinquents. 
The officers belonging to the tower of London 
consist of 
1 Constable and chief govern- 
or, at - 
1 Lieutenant governor, at 
I Deputy lieutenant, at 
1 Major, at 
1 Chaplain, at - 
1 Gentleman porter, at 
1 Gentleman gaoler, at 
1 Physician, at - 
1 Surgeon, at 
1 Apothecary, 1 yeoman porter. 
per annum. 
£ 1000 0 
700 0 
365 0 
182 10 
121 13 
84 6 
70 0 
182 10 
45 12 
Tower-bastions , in fortification, are small 
towers made in the form of bastions, by M. 
Vauban, in his second and third method ; 
with rooms or cellars underneath to place 
men and guns in them. 
Towers, moveable, in antient military his- 
tory, were three stories high, built with large 
beams : each tower was placed ou four wheels 
or trucks, and towards the town covered 
with boiled leather, to guard it from fire, and 
to resist the darts ; on each story one hun- 
dred archers were posted. They were push- 
ed with the force of men towards to the city 
wall. From these the soldiers, placed in the 
different stages, made such vigorous dis- 
charges that none of the garrison dared to 
shew themselves on the rampart. 
I OXICODEN DRON, the poison-wood. 
See Rhus. 
TOZZIA, a genus of the didynamia an- 
giospermia class of plants, with a monopelal- 
ous ringent flower ; the upper lip of which is 
bifid, and the lower one trifid ; the fruit is a 
globose unilocular capsule, containing an 
ovated seed. One species. 
TRACHEA. See Anatomy, 
TRACHELIUM, a genus of the pentan- 
dria monogynia class of plants, with a funnel- 
•T ft A 
j fashioned flower, divided into Are Segment* 
j at the limb ; the fruit is a roundish obtusely 
trilobous capsule, containing a great number 
of very minute seeds. There are three spe- 
cies, herbs of the Levant. 
1 RACHICHTH YS, a genus of fishes of 
the order thoracici. The generic character 
is, head rounded in front ; eyes large ; mouth 
wide, toothless, descending ; gill-membrane 
with eight rays, the four lowermost of which 
are rough on the edges ; scales rough ; ab- 
domen cataphracted with large carinate 
scales. There is only a single species, viz. 
the australis, that inhabits "New Holland, 
about five inches long, and two deep ; body- 
coated with scales so strongly and closely in- 
serted, that it is not possible to detach one 
from the rest without bringing with it a por- 
tion of the skin. 
TRACIIINUS, Weever, a genus of 
fishes of the order jugulares : the generic 
character is, head slightly roughened, com- 
pressed; gill-membrane six-rayed; gill-covers 
serrated on the edge ; body compressed, 
vent situated near the breast. 
: 1. Tfachinus draco, dragon weever. This 
fish is of £ lengthened shape, much compress- 
ed on the sides, and covered with small and 
easily deciduous scales ; the mouth is wide, 
and opens vertically, like that of the star- 
gazer ; both jaws are armed with sharp teeth; 
the tongue is straight, smooth, and pointed ; 
the eyes are seated on the upper part of the 
head, pretty near each other ; the gill-covers 
are armed at their tips witlr-a strong spine. 
The general colour of the weever is silvery-, 
with a yellowish or dusky cast on the upper 
parts, while the sides are commonly varied 
by numerous obliquely transverse streaks of 
a similar colour ; the scales are small and 
rounded ; the first dorsal fin is of a deep 
black. The usual length of the fish is about 
ten or twelve inches. 
This fish is an inhabitant of the Mediter- 
ranean and Northern seas, commonly fre- 
quenting the coasts, and frequently imbed- 
ding itself in the sand ; in which situation, if 
accidentally trodden on, it strikes backwards 
with great violence, and endeavours to wound 
the aggressor with the spines of its first dorsal 
fin. So troublesome are the consequences 
arising from the punctures inflicted by this 
part, that a law is said to exist in France, 
obliging the fishermen to cut it away before 
the fish is exposed for sale. The usual 
symptoms attending the wound are, violent 
heat, pain, and inflammation ; and it not un- 
frequently happens that when the hand is 
thus wounded, a sudden redness extends 
throughout the whole length of the arm, as 
far as the shoulder. The usual remedy 
among the English fishermen is, according to 
Mr. Pennant, sea-sand, well rubbed on the 
part : an application which one might at first 
suppose would rather aggravate than alleviate 
the complaint. Many other popular remedies 
are used in different countries. Notwith- 
standing the suspicious aspect of the above- 
mentioned black fin, it does not seem to have 
any thing in its conformation which can jus- 
tify the idea of any poisonous fluid conveyed 
from it into the wound; the spines when 
microscopically examined shewing no ap- 
pearance ©fa tubular structure. 
The weever is considered as an excellent 
article of food, and is much esteemed in 
Holland, France, &c. It feeds principally 
