TEC 
tears are these : 1. They contiinially moisten 
the surface of the eye and eye-lids, to pre- 
vent the transparent cornea from drying and 
becoming opaque, or the eye from concret- 
ing with the eye-lids. 2. They prevent that 
pain whicli would otherwise arise from the 
friction of the eye-lids against the ball of tile 
eye from continually winking. 3. They wash 
kway dust, or any thing acrid, that may 
have fallen into tlie eye. This liquid is 
transparent and colourless, has no percep- 
tible smell, but a saline taste. It communi- 
cates to vegetable blues a permanent green 
colour. When it is evaporated nearly to 
dryness, cubic crystals are formed, which 
are muriate of soda. Soda is in excess, be- 
cause vegetable blues are converted by it 
to a green colour. A portion of mucilagi- 
nous matter, which becomes yellow as it 
dries, remains after the evaporation. This 
liquid is soluble in water, and in alkalies. 
Alcohol produces a white flaky precipitate, 
and when it is evaporated, muriate of soda 
and soda remain behind. By burning the 
residuum, some traces of phosphate of lime 
and of soda are detected. The component 
parts of tears are therefore, 
Water, Muriate of soda, 
Mucilage, Phosphate of lime. 
Soda, Phosphate of soda. 
The mucilage of tears absorbs oxygen 
from the atmosphere, and becomes thick, 
viscid, and of a yellow colour. It is then 
insoluble in water. Oxymuriatic acid pro- 
duces a similar effect. It is converted into 
muriatic acid, so that it has been deprived 
of its oxygen. The mucus of the nose con- 
sists of the same substances as the tears ; 
but being more exposed to the air, it ac- 
quires a greater degree of viscidity from 
the mucilage absorbing oxygen. 
TECHNICAL expresses somewhat re- 
lating to arts or sciences : in this sense we 
say technical terms. It is also particularly 
applied to a kind of verses wherein are con- 
tained the rules or precepts of any art,4h’us 
digested to help the memory to retain them ; 
an example whereof may be seen in the 
article Memory. 
TECTONA, in botany, a ghniis of the 
Pentandria Monogynia class and order. 
Natural order of Vitices, Jussieu. Essen- 
tial character : corolla five-cleft ; stigma 
toothed ; drupe dry, spongy, within the in- 
flated calyx; nut three-celled. There is 
only one species ; viz. T. grandis, teak 
wood, or Indian oak ; the trunk of this tree 
grows to an immense size ; bark ash-colour- 
TEL 
ed ; branches cross-armed, numerous, spread- 
ing ; young shoots four-sided ; leaves oppo- 
site, above scabrous, beneath covered with 
soft white down ; the leaves on young trees 
from twelve to twenty-four inches long, and 
from eight to sixteen broad ; petiole short, 
thick, laterally compressed ; panicle termi- 
nating, very large, cross-armed ; divisions 
dichotomous, with a sessile fertile flower in 
each cleft : the whole covered with a hoary 
farinaceous substance ; flowers small, white, 
very numerous, fragrant ; nectary very small ; 
nut exceedingly hard, four-celled. It is a 
native of the large forests in Java and Cey- 
lon, Malabar, Coromandel, Pegu, Ava, the 
confines of Cochinchina, and Cambodia, 
&c. The wood of this tree has by long ex- 
perience been found to be the most useful 
timber in Asia ; it is light, easily worked, 
and at the same time both strong and dura- 
ble ; for ship building the teak is reckoned 
superior to any other sort of wood. A du- 
rable vessel of burthen cannot be built in 
the river of Bengal, without the aid of teak 
plank ; some of the finest merchant ships 
ever seen on the river Thames have arrived 
from Calcutta, where they were built of 
teak timber. 
TEETH. See Anatomy. Teeth have been 
analyzed by Mr. Pepys, who has found the 
constituent parts of teeth of different ages 
to be, in different proportions : phosphate 
of lime, carbonate of lime, and cartilage. 
According to Fourcroy and A^auquelin, 
the enamel is composed of 
Phosphate of lime 72.9 
Gelatine and water 27.1 
100 
TELEGRAPH, a word derived from 
the Greek, and which is very properly 
given to an instrument, by means of which 
information may be almost instantaneously 
conveyed to a considerable distance. The 
telegraph, though it has been generally 
known and used by the moderns only for a 
few years, is by no means a modern in- 
vention. There is reason to believe that 
amongst the Greeks there was some sort of 
telegraph in use. The burning of Troy was 
certainly known in Greece very soon after 
it happened, and before any person had re- 
turned from thence. Now that was alto- 
gether so tedious a piece of business, that 
conjecture never could have supplied the 
place of information. A Greek play begins 
witli a scene in which a watchman descends 
from the top of a tower in Greece, and 
