7SS T E T 
9 
tial says that beds were inlaid with it. Juve- 
nal, and Apuleius in his tenth book, mention 
that the Indian bed was all over shining with 
tortoise-shell on the outside, and swelling 
with stuffing of down within. The immense 
use made of it in Rome may be guessed at by 
what we 'earn from Velleius Paterculus, who 
says, that when Alexandria was taken by Ju- 
lius Caesar, the magazines or warehouses 'were 
so full of this article, that he proposed to have 
made it the principal ornament of his triumph, 
as he did ivory afterwards, when triumphing 
for having happily finished the African war. 
This too, in more modern times, was a great 
article in the trade to China.” 
It may be doubted however, whether the 
species described and figured by Mr. Bruce, 
and said to inhabit the Red Sea, is the real T. 
imbricata ; since it appears to differ in some 
respects from the usual character of this ani- 
mal, and particularly in not having imbricated 
scales. 
Testudo, in the military art of the an- 
tients, was a kind of cover or screen which 
the soldiers, e. gr. a whole company, made 
themselves of their bucklers, by holding them 
up over their heads, and standing close to 
each other. This expedient served to shel- 
ter them from darts, stones, &c. thrown upon 
them, especially those thrown from above, 
when they went to the assault. 
Testudo was also a kind of large wooden 
tower which moved on several wheels, and 
was covered with bullocks’-hides, serving to 
shelter the soldiers when they approached 
the walls to mine them, or to batter them 
with rams. 
TETHYS, a genus •!' insects belonging to 
the class of vermes, and order of mollusca. 
The body is oblong, fleshy, and without feet; 
the mouth consists of a cylindrical proboscis 
under the duplicature of a lip ; and there are 
two foramina at the leftside of the neck. The 
species are two, both inhabitants of the 
ocean. 
TETRACERA, a genus of plants of the 
class polyandria, and order tetragynia, and 
in the natural system ranging under the doubt- 
ful. The calyx is hexaphyllous, and the 
capsules four. There are 12 species, shrubs 
of South America. 
TETRACHORD, in music, (from the 
Greek,) a concord in the music of the antients 
consisting of three degrees, or intervals, and 
four terms, or sounds ; called by the Greeks 
also diatessaron, and by us a fourth. In this 
system the extremes were fixed, but the mid- 
dle sounds were varied according to the 
mode. 
In the antient music, all the primitive or 
chief divisions were confined to four chords, 
so that the great scale consisted of replicates, 
and all the upper tetrachords were considered 
only as repetitions of the first or lowest. 
TETRADIAPASON, the Greek appella- 
tion of the quadruple octave, which we also 
call the 29th. The system of the antients 
not extending to this interval, they only knew 
it in imagination, or by name. 
TETRADYNAMIA (Tiaaccet;, four, and 
ivvatfMf, power), four powers; the name of 
the 15th class in Linnaeus’s sexual system. 
See Botany. 
T E T 
( tetraedron, or Tetrahedron, in geo. 
j metry, is one of the five Platonic or regular bo- 
dies or solids, comprehended under four equi- 
lateral and equal triangles. Or it is a triangular 
pyramid of four equal and equilateral faces. 
it is demonstrated in geometry, that the side 
of a tetraedron is to the diameter of its circum- 
scribing sphere, as to ; consequently 
they are incommensurable. 
If a denotes the linear edge or side of a tetrae- 
dron, b its whole superficies, c its solidity, r the 
radius of its inscribed sphere, and R the radius 
of its circumscribing sphere ; then the general 
relation among all these is expressed by the fol- 
lowing equations, viz. 
« = 2 V.6 = fRfy 6 = vTV 3 = 
\/ 6 ‘V 2 . 
b — 24 rV3= 3 RV 3 = <2 V 3 = 
6(/YV3. 
c = 8 rV 3 — ARV 3 — tWa/ 2 = 
V2V3. 
R — Sr = £«v/' 6 — 4 a/ 2 b\/3 — 
r — yR — — sTa/^a / 3 — • 
i^lV 3 - 
TETRAGONIA, a genus of plants of the 
class of icosandria, and order monogynia; 
and in the natural system ranging under the 
13th order, succulents. The calyx is di- 
vided into three, four, or five parts. There 
is no corolla ; the drupe is beneath, and the 
nut three or eight-celled. There are eight 
species ; the puticosa, decumbens, herbacea, 
echinata, expansa, crystallina, hirsuta, and 
spicata, chiefly natives of the Cape. 
TETRAGYNIA (recr<r«f£ r, four, and <yvrn, 
a woman), the name of an order, or seconds- i 
x’y division, in the 4th, 5th, 6th, 8th, and 13th | 
classes in the sexual system. See Botany. 
TETRALOMA, a genus of insects of the 
coleoptera order. The generic character is, 
antennae clavate, the club perfoliate, less 
rounded, entire; feelers thickish, unequal; 
shells as long as the abdomen. There are two 
species of this insect, viz. the T. fungorum, 
and the T. ancora. 
TETRANDRIA four, and 
a man or husband), the name of the fourth 
class in Linnaeus’s sexual system. See Bo- 
tany. 
TETRANTHUS, a genus of the synge- 
nesiapolygamia segregata class and order of 
plants. The calyx is common, four-flowered ; 
perianthium proper, one-leafed ; seeds crown- 
ed. There is one species, au annual of His- 
paniola. 
TETRAO, in ornithology, a genus of 
birds belonging to the order of gallinae, and 
thus characterised by Linnaeus : there is a 
spot near the eyes naked or papillose, or co- 
vered, though more rarely, with feathers. 
Gmelin has enumerated about 66 species. 
Thegenustetraocomprehendsboththe grouse, 
partridge, and quail ; but Dr. Latham, with j 
great judgment and piopriety, has made two 
genera of them, under the names of tetrao, 
comprehending the grouse; and perdix, com- 
prehending the partridge and quail. Dr. 
Latham thus distinguishes the genus tetrao : 
the bill is like a crooked cone, with a naked 
scarlet skin above each eye, and the feet fea- 
thered to the toes. The perdix he character- 
TEt 
izes by a bill convex, strong, and short ; the' 
j nostrils are covered above with a callous pro. 
I minent rim; the orbits are papillose ; the 
j feet naked, and most of the species are’ fur- 
i nished with spurs. He reckons twenty spe- 
| cies under the tetrao, and forty-eight under 
the perdix. 
I. Tetrao. Of this genus the following 
: species are found in Britain : 1 . The urogaL 
j lus, or cock of the wood, inhabits woody and 
mountainous countries; in particular, forests 
j of pines, birch-trees, and junipers; feeding on 
j the tops of the former, and berries of the & lat- 
j ter ; the first often infects the flesh with such 
a taste as to render it scarcely eatable. In 
the spring it calls the females to its haunts 
with a loud and shrill voice; and is at that 
time so very inattentive to its safety, as to be 
very easily’ shot. It stands perched on a 
tree, and descends to the females on their 
first appearance. They lay from eight to 
sixteen eggs ; eight at the first, and more as 
they 7 advance in age. 
This bird is common to Scandinavia, Ger- 
many, France, and several parts of the Alps. 
It is found in no other part of Great Britain 
than the Highlands of Scotland, north of In- 
verness ; and is very rare even in those 
parts. 
The length of the male is two feet nine 
inches ; its weight sometimes fourteen pounds. 
The female is much less, the length being 
j only twenty-six inches. The sexes differ also 
j greatly in colours. The bill of the male is of 
! a pale yellow ; the head, neck, and back, are 
: elegantly marked, slender lines of grey and 
black running transversely. The upper part 
of the breast is of a rich glossy green ; the 
rest of the breast and belly black, mixedwith 
some white feathers ; the sides are marked 
like the neck ; the coverts of the wings cross- 
ed with undulated lines of black and°reddish 
brown ; the exterior webs of the greater 
quill-feathers are black: the tail consists of 
eighteen feathers, the middle of which is the 
longest; these are black, marked on each 
side with a few white spots. The legs are 
very strong, and covered with brown feathers ; 
the edges of the toes are pectinated. Of the 
female, the bill is dusky; the throat red ; 
the head, neck, and back, are ma> ked with 
transverse bars of red and black: the breast 
has some white spots on it, and the lower part 
is of a plain orange-colour ; the belly is bar- 
red with pale -orange and black ; the tips of 
the feathers are white. The tail is of a deep 
rust-colour, barred with black, tipped with 
white, and consists of sixteen feathers. 
2. The tetrix, black grouse, or black-cock, 
like the former species, is fond of woody and 
mountainous situations ; feeding on the vac- 
cinum, arid other mountain-fruits, and in the 
winter on the tops of the heath. In the sum- 
mer they frequently descend from the hills to 
feed on corn. They never pair: but in the 
spring the male gets upon some eminence, 
crows and claps his wings ; on which signal 
ail the females within hearing resort to him. 
The hen lays seldom more than six or seven 
eggs. When the female is obliged, during 
the time of incubation, to, leave her eggs in 
quest of food, she covers them up so artfully 
with moss or dry leaves, that it is very dif- 
ficult to discover them. On this occasion she 
is extremely tame and tranquil, however wild 
and timorous at other times. She often keens, 
, * 
