TID 
of insects of the order Hymenoptera ; month 
horny, willf an incurved mandible, the jaw 
short and straight ; lip longer than the jaw, 
membranaceous at the tip, and trilid, the 
middle division emarginate ; tongue very 
short, involute ; four feelers, equal, filiform; 
antennae cylindrical, the first joint tliicker. 
I’here are four species : three of New Hol- 
land, and one of Africa. Specimens of them 
all are to be found in Sir Joseph Banks’s 
museum. 
TIARELLA, in botany, a genus of the 
Decandria Digynia class and order. Natu- 
ral order of Succulentae. Saxifragae, Jus- 
sieu. Essential character : calyx five-parted; 
corolla five petalled, inserted into the calyx ; 
petals entire ; capsule one-celled, two-valv- 
ed, with one valve larger. There are two 
species ; viz. T. cordifolia, heart-leaved tia- 
rella ; and T. trifoliata, three-leaved tiarella, 
both natives, of the northern parts of Ame- 
rica and Asia. 
TIDES, two periodical motions of the 
waters of the sea, called the flux and reflux, 
or the flow and ebb. The cause of the tides 
is the attraction of the sun and moon, but 
chiefly of the latter; the waters of the im- 
mense ocean, forgetful, as it were, of their 
natural quietus, move and roll in tides, obse. 
quious to the strong attractive power of the 
moon, and W'eaker influence of.the sun. See 
Astronomy. 
That the tides may have their full motion, 
the ocean in which they are produced ought 
to be extended from east to west 90°, or a 
quarter of a great circle of the earth, at 
least ; because the places where the moon 
raises most, and most depresses the water, 
are at that distance from one another. 
Hence it appears, that it is only in the great 
oceans that such tides can be produced ; 
and wily, in the large Pacific ocean, they 
exceed those in the Atlantic ocean ; hence 
also it is obvious, why the tides ar,e not so 
great in the torrid zone, between Africa and 
America, whpre tlie ocean is narrower, as 
in the temperate zones on either side ; and 
from this also, we may understand why the 
tides are so small in islands that ai e very far 
distant from tlie shores. It is manifest, 
that, in the Atlantic ocean, the water can- 
not rise on one shore but by descending on 
the other; so that, at the intermediate dis- 
tant islands, it must continue at about a 
mdan height between its elevation on the 
one and on the other shore. As the tides pass 
over shoals, and run through streights into 
bays of the sea, their motion becomes more 
various, and their height defends on a great 
VOL. VI. 
TID 
many circumstances. The tide that is pro- 
duced bn the western coast of Europe cor- 
responds to the theory above described : 
thus, it is high water on the coast of Spain, 
Portugal, and the West of Ireland, about 
the third hour alter tlie nrtoon has passed 
the meridian : from thence it flows into the 
adjacent channels, as it finds the easiest 
passage. One current from it, for example, 
runs up by the soutli of England, and ano- 
ther comes in by the north of Scotland : 
they take a considerable time to move all 
tins tvay', and it is high water soonei* in the 
places to which they first come ; and it be- 
gins to fall at those places, while the twm 
currents are yet going on to others that are 
further in their course. As they return, 
they are not able to raise a tide ; because 
the water runs faster otf than it returns, til 
by a new tide propagated from the ocean, 
the return qf the current is stopped, and tlie 
water begins to rise again. The tide takes 
twelve hours to come from the ocean to 
London bridge, so that, when it is high W’ater 
there, a new tide is already come to its 
height in the ocean ; and, in some interme- 
diate place, it must be low water at the 
same time. In channels, therefore, and 
narrow seas, the progress of the tides may 
be, in some respects, compared to the mo- 
tion of the waves of the sea. It may 
be observed, that when the tide runs over 
shoals, and flows upon flat shores, the water 
is raised to a greater height than in the open 
and deep oceans that have steep banks; 
because the force of its motion cannot be 
broken, upon these levelshores, till the water 
rises to a greater height. If a place com- 
municates with two. oceans (or two different 
ways witli the same ocean, one of which is 
a readier and easier passage) two tides may 
arrive at that place in different times, which, 
interfering with each other, may produce a 
greater variety of phenomena. 
An extraordinary instance of this kind 
is mentioned at Bathsha, a port in the 
kingdom of Tonquin in the East Indies, of 
northern latitude 20“ 50'. The day in which 
the moon passes the equator, the w’ater 
stagnates there without any motion : as the 
moon removes from the equator, the water 
begins to rise and tall once a day; and it is 
high water at the setting of the moon, and 
low water at her rising. This daily tide in- 
creases for about seven or eight days, and 
then decreases for as many days by the same 
degrees, till this motion ceases when the 
moon has returned to the equator. When 
she has passed the equator, and deeiines to- 
D d 
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