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that it can be completely separated from the 
straw. 
But though, when the size of the machine 
is considerable, the expence of erecting it 
may be from eighty to one hundred pounds, 
according to situation and materials, smaller 
ones may be erected at much less, as from 
thirty to fifty pounds. 
Some of this kind of mills have rollers or 
small mill-stones added to them, for the pur- 
pose of crushing and grinding grain for horses, 
swine, and other animals ; and also instru- 
ments for cutting straw into chaff. 
On the necessity of employing machines 
of this kind, it is remarked by an able writer, 
that it is the only method left for having the 
corn cleanly and properly thrashed. They 
are so quick in the work, that the whole may 
be done under the eye of the master, and the 
corn secured in the granary without the least 
pilfering. The saving, by this means of 
thrashing, in the extra quantity of corn pro- 
cured, and tire security against having the 
corn stolen in the chaff, it is asserted, amounts 
to an advantage in favour of the mills of 
about ten per cent on the corn-crops ; in 
some cases, to one shilling a bushel oa wheat, 
and very generally to twenty shillings' an acre 
on the wheat-crops. 
This machine has undoubtedly many ad- 
vantages over the flail, as well as those of 
saving time and hands ; as in thrashing damp 
corn, not capable of being fully accomplished 
in any other way, especially in wet seasons ; 
and with smutty wheat, which is thrashed by 
it without any mischief being done to the 
sound grain, the smut not being crushed 
conies out whole, and is blown away with 
the chaff. 
The principal objections that have been 
made to these machines, are the great expence 
of erecting and using them, their tendency to 
diminish the labour of the poor, and their 
affording; too great a supply of straw at a 
time. These objections are, however, of 
little consequence, when the general utility 
and advantages of such machines are con- 
sidered ; besides the latter are either such as 
have nothing to be apprehended from them, 
or as may be readily obviated. The diffi- 
culty in regard to the straw may be easily 
removed, by having it properly stacked up 
©r cut into chaff. 
THRAVE, or Threave of corn, twenty- 
four sheaves, or four shocks of six sheaves 
to the shock, though, in some counties, 
they only reckon twelve shocks to the thrave. 
THREAD, a small line made up of a 
number of fine fibres of any vegetable or ani- 
mal substance, such as flax, cotton, or silk ; 
from which it takes its name of linen, cotton, 
er silk thread. 
Linen and cotton thread may be dyed of 
a durable and deep black by a solution of iron 
in sour beer, in which the linen is to be steeped 
for some time, and afterwards boiled in mad- 
der. See ,t he article Dyeing. Thread may 
be easily bleached by the oxymuriatic acid 
discovered by Mr. Scheele. 'This acid whit- 
ens cloth remarkably well, but it is still more 
advantageous for bleaching thread. 
THREATENING LETTER. If any 
person shall send any letter threatening to 
accuse any other person of a crime punish- 
able with death, transportation, pillory, or 
other infamous punishment, with a view to 
extort money from him, he shall be punished 
at the discretion of the court, with fine, im- 
prisonment, pillory, whipping, or transpor- 
tation. 80 G. ll.c. 24. But if the writer of 
a threatening letter delivers it himself, and 
does not send it, tie is guilty of felony under 
this act. Leach’s Cro. Law, 351. 
THRINAX, small Jamaica fan-palm ;'a '• 
genus of plants of the natural class of palma | 
and order of flabelhfolire. The calyx is sex- j 
dentate ; there is no corolla ; there are six ! 
stamina ; the stigmas are emarginale, and 
the berry monospermous. This plant was i 
the form of a flatfish, smooth, irregular exsu- 
dation, of a yellow colour, on various parts of 
the plant. See Triticum. The ingenious Mr. 
Kirby, however, seems convinced that the 
lliiips is in reality an insect highly injurious 
to corn, by deriving its nourishment from the 
embryo grains. There are eight species. 
THRUSH. Seed urdus. 
THRYALLIS, a genus of plants of the 
class decandria, and order monogynia ; and 
in the natural system ranging under the 38th 
order, tricocca?. The calyx is quinquepar- 
brougbt from Jamaica to Kew gardens by j life, there are five petals, and the capsule is' 
Dr. William Wright 
THRIPS, a genus of the order hemipteva: 
the generic character is, snout inconspicuous ; 
antennae the length of thorax ; body linear, 
abdomen reflexile upwards ; wings four, 
straight, long, narrow, inc unbent on the 
back, slightly crossed. This is a genus con- 
sisting of very small insects, which are prin- 
cipally found on flowers. The antennae are 
submoniliform, and of the length of the tho- 
rax ; the snout is obscure or inconspicuous, 
short, and placed beneath the neck or head ; 
the body of a lengthened or sublinear shape, 
and the abdomen is at pleasure bent upwards 
or backwards ; the wings are four iu number, 
long, narrow, incumbent, and very slightly, 
or scarcely, crossed over each other. 
The most familiar example of the genus is 
the tlirips physapus of Linnaeus, which is a 
very small slender insect, of a black colour, 
very frequently seen during the spring and 
summer on various flowers, more especially 
on what are termed the compound flowers, 
as dandelion, &e. It wanders about the pe- 
tricoccous. There is only one species 
known, the brasiliensis, a shrub of Brasil. 
TH UJ A, the arbor vita;, a genus of plant's 
1 of the class monadelphia, and order monoecia ; 
| and in the natural system ranging under the 
I 51st order, conifer*. There are four species 
| known; the orientalis, occidentafis, articulata, . 
j and dolabrata; of which the two first are 
i most remarkable. 1. The occidenlalis or 
! common arbor vita?, grows naturally in Ca- 
nada, Siberia, and other northern countries. 
In some of the English gardens a few of these 
trees are to be met with of a large size ; it has 
a strong woody trunk, which rises to the 
height of 40 feet or more. T he bark, while ■ 
1 young, is smooth, and of a dark-brown colour ; 
I but as the trees advance, the bark becomes . 
j cracked, and less smooth. The branches 
j are produced irregularly on every side, 
I standing almost horizontal, and the young 
slender shoots frequently hang downward, 
thinly garnished with leaves ; so that when 
the trees are grown large, they make but an 
indifferent appearance. The leaves of this 
tals of the flower, descending to the bottom i tree have a rank oily scent when bruised, 
of the florets, occasionally emerging at in- | 2. The orientalis, or China arbor vitae, grows 
tervals, and often skipping from place to naturally in the northern parts of China, 
place, in performing which action it is ob- : where it rises to a considerable height ; but 
served suddenly to turn back its abdomen 
so as nearly to touch the thorax with its tip. 
this has not been long enough in Europe to 
have any trees of large size. The seeds of 
The wings are of a semitransparent white, this sort were first sent to Paris by some of 
narrow, and when properly magnified, are the missionaries ; and there are several of the 
observed to be edged and tipped with hairs trees growing in the gardens of the curious 
growing gradually longer as they approach 
the tips, where they are of considerable 
length : the lower wings are rather shorter 
than the upper, beneath which they are, in 
general, almost concealed ; the antennae 
consist of six joints, and the feet are tipped 
with an expansile and apparently vesicular 
process, enabling the little animal to adhere 
there, which an more than twenty feet high. 
The branches of this sort grow closer toge- 
ther, and are much better adorned with . 
leaves, which are of a- brighter-green colour, 
so as to make a better appearance than the 
other ; and being very hardy, it is esteemed 
preferable to most of the evergreen trees - 
with small leaves, for ornament in gardens. 
at pleasure with the greater security to any ! These trees are propagated by seeds, layers. 
particular substance. All these particulars 
require a microscope for their investigation, 
or cuttings. 
THDMMERSTONE. 
This stone was 
near Balme D’auris in Dauphine, and gave it 
the name of shorl viole. It was aftei wards 
found nearThuin in Saxony, in consequence 
of which Werr.e- called it thummerstone. 
It is sometimes amorphous, but more com- 
monly crystallized. 4 he primitive form of 
the whole insect not exceeding the tenth of first described by Mr. Schreber, who found it 
an inch in length. The larva in a great de- 1 
gree resembles the complete insect, but is 
destitute of wings; when very young it is 
white, and aftei wards of a yellowish or red- 
dish colour, and like the complete insect, is 
seen wandering about the petals of flowers. 
The thrips physapus has been supposed to its crystals is a rectangular prism, whose 
do much injury to wheat, rye, &c. by causing i bases re par Jlelograms with angles of 101° 
the young flowers to decay, thus preventing j 32 an 1 78° 28. The most usual variety is a 
the growth of the embryo grain. This opi- flat rhomboidal paradelopiped, with two of-' 
nion, however, has by some been Considered- its opposite edges wanting, and a small face 
as erroneous; who have contended that the in place of each. The faces of theparallelo- ■ 
thrips does not attach itself to such of the piped are generally streaked longitudinally. 
The texture of thummerstone is foliated. 
Its fracture conehoidal. Glassy. Causes 
simple refraction. Specific.-gravity 3.2956, 
Colour clove-brown » sometimes inclining to 
red, green, grey, violet, or black. Before 
the blowpipe it froths like zeolite, and melts 
cereal ia as are in a perfect healthy state, but 
rather to such as are diseased by having the 
germina covered with the dust of a very 
minute fungus, often growing on wheat, &c, 
and belonging to the genus tecidium or lyco- 
perdon, and which makes its appearance in 
