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trance, the other affording them an outlet. 
The banks of some rivers are often perforated 
with them. When the waters decrease, they 
dig fresh holes lower down, in order to enjoy 
their element the water. The season and 
hour when the chrysalids of the different spe- 
cies of the ephemeras turn into Hies, main- 
tain a kind of regularity. The heat, the rise 
or fall of the waters, accelerate, however, or 
postpone their final display. The ephemera 
of the Rhine appear in the air two hours be- 
fore sunset. These flies are hatched almost 
all at .the same instant in such numbers as to 
darken the air. The most early of those on 
the Marne and Seine in France do not begin 
to lly till two hours after tire setting of the 
sun, towards the middle of August. They 
are seen fluttering and sporting on the brink 
of their tomb. The glare of light attracts 
them, round which they perform a thousand 
circles with amazing ' regularity. Their 
coining together for the purpose of genera- 
tion can only be surmised, the shortness of 
their life requiring that all its functions should 
be proportionable to their duration. Some 
naturalists have been of opinion, that the 
males impregnate the eggs after the manner 
of lishes. The females, by the help of the 
threads of their tail and the flapping of their 
wings, support themselves on the surface of 
the water, and in that almost upright situa- 
tion drop their eggs in clusters. One single 
female will lay 700 or 800 eggs, which sink 
to the bottom. The larvae that escape from 
the voraciousness of the fishes, set about the 
construction of habitations to shelter them 
from every kind of danger. When the llies 
have propagated, they are seen to die, and 
fall by heaps. The land and water are strew- 
ed with them to a considerable thickness. 
The fishermen consider these multitudes of 
destroyed insects as manna for the lishes. 
See Plate Nat. Hist. fig. 180. 
Ephemera, in medicine, the name of a 
species of fever continuing the space of one 
day, or sometimes more ; for medical writers 
express themselves bv ephemera simplex, 
vel plurium dierum. See Medicine. 
Ephemera maligna, is also a term by 
which some authors have called the sudor 
Anglicanus, or malignant diary fever, which 
generally destroyed the patient in 24 hours. 
EPHEMEltfDES, in astronomy, tables 
calculated by astronomers, shewing the pre- 
sent state of the heavens for every day at 
noon ; that is, the places wherein all the 
planets are found at that time. It is from 
these tables that the eclipses, conjunctions, 
and aspects of the planets, are determined; and 
horoscopes or celestial schemes constructed. 
■In England, the Nautical Almanac, or As- 
tronomical Ephemeris, published annually by 
anticipation, under the direction of the com- 
missioners of longitude, is the most consider- 
able. In France, celestial ephemerides 
were published by M, Desplaces every ten 
years, from 1715 to 1745: they were after- 
wards continued by the abbe Caille, with 
many additions ; of which an account may 
be seen in the History of the Academy of 
Sciences for 1748. The Academy of 'Sci- 
ences have likewise published annually, 
from the beginning of the last century, *a 
kind of ephemeris, under the title of Con- 
noiss.mce des Terns, 
EPHIEUS, a genus of the class and order 
octandria monogynia, The calyx is five- 
parted; petals five-clawed ; nect. ten scales ; 
capsule oblong. There is one species, a tree 
of Guiana. 
EPHOD, in Jewish antiquity, one part of 
the priestly habit ; being a kind of girdle, 
which, brought from behind the neck over 
the two shoulders, and hanging down before, 
was put across the stomach, then carried 
round the waist, and made use of as a girdle 
to the tunic. 
There were two sorts of epliods, one of 
plain linen for the priests, and the other em- 
broidered for the high-priest. Of this last 
Moses gives an ample description. It was 
composed of gold, blue, purple, crimson, and 
twisted cotton. Upon part of it, which pass- 
ed over the shoulders, were two large pre- 
cious stones, one on each shoulder: upon 
these were engraved the name of the twelve 
tribes, six upon each stone. 
The ephod was peculiar to the priesthood, 
and thought essential to their character ; it 
being the opinion of the Jews, that no wor- 
ship," true or false, could subsist without a 
priesthood and ephod. 
EPIIORI, in Grecian antiquity, magis- 
trates established in antient Sparta to balance 
the regal power. The authority of the ephori 
was very great. They sometimes expelled 
and even put to death the kings, and abo- 
lished or suspended the power ot the other 
magistrates, calling them to account at plea- 
sure. There were five of them, others say 
nine. They presided in the public shews 
and festivals. They were entrusted with the 
public treasure, made war and peace, and 
were so absolute, that Aristotle makes their 
government equal to the prerogative of a 
monarchy. They were established by Ly- 
curgus. 
EP1BATERTUM, a genus of the monoe- 
cia hexandria class and order. The calyx is 
double; petals six; drupes three, subglobu- 
lar, muconate, &c. There is but one species. 
EPIC, or heroic poem. See Poetry. 
EPICEDIUM, in antient poetry, a poem 
rehearsed during the funeral solemnity of 
persons of distinction. We find two beau- 
tiful epicediums in Virgil, one of Eurvalus, 
and the other of Pallas, 
EPICHIREMA, in logic, a mode of rea- 
soning, which comprehends the proof of one 
or both the premises of a syllogism, before 
the conclusion is drawn. 
EPICCEN E, in grammar, a term applied 
to nouns, which, under the same gender and 
termination, mark indifferently the male and 
female species. 
EPICYCLE, in the antient astronomy, a 
little circle whose centre is in the". circum- 
ference of a greater circle ; or it is a small 
orb, or sphere, which being fixed in the de- 
ferent of a planet, is carried along with it ; 
and vet, by its own peculiar motion, carries 
the planet fastened to it round its proper 
centre. It was by means of epicycles that 
Ptolemy and his followers solved the various 
phenomena of the planets, but more espe- 
cially their stations and retrogradations. 
The great circle they called the excentric 
or deferent, and along its circumference the 
centre of the epicycle was conceived to 
move ; carrying with it the planet fixed in its 
circumference, which in its motion down- 
wards proceeded according to the order of the 
signs, but, in moving upwards, contrary to 
that order. The highest point of a planet’s 
E P I 
epicycle they called apogee, and the lowest 
perigee. 
■ The length of any part of the curve of an 
epicycloid, which any given point in the re- 
volving circle has described, from the posi- 
tion where it touched the circle upon which 
it revolved, is to double the versed sine of 
half the arc which all the time of revolving 
touched the quiescent circle, as the sum of 
the diameters of the circles, is to the semi- 
diameter of the quiescent circle in the exte- 
rior cycloid ; or as the difference of the dia- 
meters is to that semidiameter, for the inte- 
rior one. 
Dr. Halley has given a general proposition 
for the measuring of all cycloids and epicy- 
cloids: thus, the area of a cycloid, or epicy- 
cloid, either primary, or contracted, or pro- 
late, is to the area of the generating circle ; 
and also the areas of the parts generated in 
those curves, to the areas of analogous seg- 
ments of the circle ; as the sum of double the 
velocity of the centre and the velocity of tho 
circular motion, is to this velocity of tlie cir- 
cular motion. See Philos. Trans. No. 218. 
EPICYCLOIDS, spherical, are formed by 
a point of the revolving circle, when its plane 
makes a constant angle with the plane of the 
circle on which it revolves. 
If a parabola roll upon another equal to- 
it, its focus will describe a right line perpen- 
dicular to the axis of the quiescent parabola ; 
also the vertex of the rolling parabola will 
describe the cissoid of Diodes ; and any 
other point of it will describe some one of 
Newton’s defective hyperbolas, having a 
double point in the like point of the quies- 
cent parabola. 
In like manner, if an ellipse revolve upon 
another ellipse, equal and similar to it, its 
focus will describe a circle, whose centre is 
in the other focus, and consequently the ra- 
dius is equal to the axis of the ellipsis ; and 
any other point in the plane of the ellipse 
will describe a line of the 4th order. 
The same may be said also of an hyper- 
bola, revolving upon another, equal and si- 
milar to it ; for one of the foci will describe 
a circle, having its centre in the other focus J 
and the radius will be the principal axis of 
the hyperbola ; and any other point of the 
hyperbola will describe a line of the 4th 
order. 
Concerning these lines, see Newton’s Prin- 
cipia, lib. i ; see also Muclaurin’s Geometria 
Organica. 
Epicycloid, in geometry, a curve ge- 
nerated by the revolution of the periphery of 
a circle, ACE (Plate Miscel. fig. 84), along 
the convex or concave side of tiie periphery, 
of another circle, DGB. 
Tiie length of any part of the curve, that 
any given point in the revolving circle has 
described, from the time it touched the cir- 
cle it revolved upon, shall he to double the 
versed sine of half the arch, which all that 
time touched the circle at rest, as the sum of 
the diameters of the circles, to the semidia- 
irieter of the resting circle, if the revolvin'* 
circle moves upon the convex side of the 
resting circle ; but if upon the concave sidel 
as the difference of the diameters, to the se- 
midiamer of the resting circle. 
EPIDEMIC. See Medicine. 
EPIDENDRUM, a genus of the diandria 
order, in the gynandria class of plants, and 
in the natural method ranking under the 7Ui 
