CLE 
colour ; is difRcultly fusible, though much 
more so than porcelain clay, from wlricli it 
is further distinguished by its superior plas- 
ticity, and the sand which it contains. It 
is manufactured into tobacco-pipes, and is 
the basis of the white or queen’s-ware pot- 
tery. Potter’s clay is of a reddisii, bluish, 
or greenish colour; has a somewhat fine 
earthy fracture, and a soft, often greasy, 
feel: it adheres to the tongue, and is very 
plastic. It burns to a hai’d, porous, red 
brick ; and in a higher heat runs into a dark- 
coloured flag. When tempered with watery 
and mixed with sand, it is manufactured in- 
to bricks : those varieties that are the most 
free from pebbles are made into tiles and 
coarse red pottery. See Alumina. 
Clay stone, in mineralogy, is of a green- 
ish, bluish, or grey colour, sometimes mark- 
ed by brownish yellow spots and stripes. 
It occurs in mass, is opaque, dull, frangible, 
and soft. It forms large mountainous masses, 
occurring in beds and veins. 
CLAYTONIA, in botany, so named in 
honour of Mr. John Clayton, a genus of the 
Pentandria Monogynia class and order. 
Natural order of Succulentae. Portulacem, 
Jussieu. Essential character: calyx two- 
valved ; corolla five-petalled ; stigma trifid ; 
capsule three-valved, one-celled, three- 
seeded. There are two species, viz, C. Vir- 
ginica and C. Sibirica. 
CLEF, or Cliff, in music, a mark set 
at the beguming of the lines of a song, 
which shows the tone or key in which the 
piece is to begin ; or it is a letter marked 
on any line, which explains the rest. It is 
called clef, or key, because hereby we 
know the names of all the other lines, and 
consequently the quantity of every degreh 
or interval : but because every note in the 
octave is also called a key, this letter 
marked is, for distinction-sake, denominated 
the signed clef ; and by this key is meant 
the principal note of a song, in which the 
melody closes. See Music. 
CLEMATIS, in botany, virgin’s botcer, a 
genus of the Polyandria Polygamia class 
and’order. Natural order of Multisilique. 
Ranunculaceas, Jussieu. Essential charac- 
ter : calyx none ; petals four, sometimes 
five, or even six ; seeds having a tail. There 
are twenty-one species. 
CLEOME, in botany, a genus of the Te- 
tradynamia Siliquosa class and order. Na- 
tural order of Putamineas. Capparides, 
Jussieu. Essential character: nectareous 
glands three, at each sinus of the calyx, ex- 
cept the lowest ; petals all ascending ; sili- 
que one-celled, two-valved. There are 
CLE 
twenty-three species, all of them natives of 
very warm countries. 
CLEONIA, in botany, a genus of the 
Uidynamia Gymnospermia class and order. 
Natural order of Verticillatse. Labiatas, 
Jussieu. Essential character : filaments 
forked, with an anther at one of the tips ; 
stigma four-cleft. There is but one species, 
viz. C. lusitanica, sweet-scented cleonia, is an 
annual plant, native of Spain and Portugal. 
CLEPSYDRA, a water-clock, or instru- 
ment to measure time by the tall of a cer- 
tain quantity of water. 
The construction of a clepsydra. To di- 
vide any cylindrical vessel into parts, to be 
emptied in each division of time, the time 
wherein the whole, and that wherein any 
part is to be evacuated, being given. Sup- 
pose a cylindrical vessel, whose charge of 
water flows out in twelve hoars, were re- 
quired to be divided into parts, to be eva- 
cuated each hour. 1. As the part of time 1 
is to the whole time 12, so is the same time 
12 to a fourth proportional 144. 2. Dividfe 
the altitude of the vessel into 144 equal 
parts: here the last will fall to the last 
hour ; the three next above to the last part 
but one ; the five next to the tenth hour ; 
lastly, the twenty-three last to the first 
hour. For since the times increase in the 
series of the natural numbers 1, 2, 3, 4, 5, 
&c. and the altitudes, if the numeration be 
in a retrograde order from the twelfth hour, 
increase in the series of the unequal num- 
bers 1, 3, 5, 7, 9, &c. the altitudes com- 
puted from the twelfth hour will be as the 
squares of the times 1, 4, 9, 16, 25, &c. 
Therefore the squares of the whole time, 
144, comprehend all the parts of the alti- 
tude of the vessel to be evacuated. But a 
third proportional to 1 and 12 is the square 
of 12, and consequently it is the number of 
equal parts in which the altitude is to be di- 
vided, to be distributed according to the 
series of the unequal numbers, through the 
equal interval of hours. There were many 
kinds of clepsydras among the ancients ; but 
they all had this in common, that the water 
ran generally through a narrow passage, 
from one vessel to another, and in the lower 
was a piece of cork or light wood, which, 
as the vessel filled, rose up by degrees, and 
showed the hour. 
CLERGY, a general name given to the 
body of ecclesiastics of the Christian 
church, in contradistinction to the laity. 
The privileges and immunities which the 
clergy of the primitive Christian church en- 
joyed, deserve our notice. In the' first 
place, when they travelled upon necessary 
