N 
t 
blage Di- chain of principles and conclusions, 
or the whole of any doctrine, the several 
parts whereof are bound together, and fol- 
low or depend on each other; in which 
sense we say, a system of pliilosophy, a 
system of divinity, &c. 
System, in astronomy, denotes an hypo- 
thesis or supposition of an arrangement of 
the several parts of the universe, whereby 
astronomers explain all the phenomena or 
appearances of the heavenly bodies, their 
motions, changes, &c. This is more pro- 
perly called the systems of the world. Sys- 
tem and hypothesis have much the same 
signification, unless perhaps hypothesis be a 
more particular system, and system a more 
general hypothesis. The three most cele- 
brated systems of the world are the Coper- 
nican, the Ptolemaic, and Tychonic. 
SYSTOLE, in anatomy, the contraction 
of the heart, whereby the blood is drawn 
out of its ventricles into the arteries ; the 
opposite state to which is called the di- 
astole, or dilation of the heart. 
S YZ\ GY, in astronomy, a term equally 
used for the conjunction and opposition of 
a planet with the sun. On the phenomena 
and circumstances of the syzygies a great 
part of the lunar theory depends. For, ] . It 
is shown in the physical astronomy, that the 
force which diminishes the gravity of the 
moon in the syzygies, is double that which 
increases it in the quadratures : so that in 
the syzygies, the gravity of the moon, from 
the action of the sun, is diminished by a 
part which is to the whole gravity as 1 to 
TAB 
89,36 : for in tlie quadratures, the addition 
of gravity is to the whole gravity as 1 to 
' 178,7'3. 2 . In the syzygies, the disturbing 
force is directly the distance of the moon 
fi'oin the earth, and inversely as the cube of 
the distance of the earth from the sun. And 
at the syzygies, the gravity of the moon to- 
wards the earth, receding from its centre, 
is more diminished than according to the in- 
verse ratio of the square of the distance 
from that centre. Hence, in the motion of 
the moon from the syzygies to the quadra- 
tures, the gravity of the moon towards the 
earth is continually increased, and the moon 
is continually retarded in its motion ; and 
in the motion from the quadratures to the 
syzygies, the moon’s gravity is continually 
diminished, and its motion in its orbit acce- 
lerated. 3. Further, in the syzygies, the 
moon’s orbit, or circle, round the earth, is 
more convex than in the quadratures, for 
which reason the moon is less distant from 
the earth at the former than the latter. 
When the moon is in the syzygies, her ap- 
sides go backwards, or are retrograde. 
When the moon is in the syzygies, the 
nodes move in antecedentia fastest : then 
slower and slower, till they become at rest, 
when the moon is in the quadratures. 
Lastly, When the nodes are come to the 
syzygies, the inclination of the plane of the 
orbit is least of all. Add that these several 
irregularities are not equal in each syzygy, 
but all somewhat greater in the conjunc- 
tion than in the opposition. 
T. 
'T' Or t, the nineteenth letter, and fif- 
J teenth consonant, of our alphabet, 
the sound whereof is formed by a strong 
expulsion of the breath through the mouth, 
upon a sudden drawing back of the tongue 
from the fore part of tlie palate, with the 
lips at the same time open. The proper 
sound of this letter is that in tan, ten, tin, 
&c. When it comes before i, followed by 
a vowel, it is sounded like s, as in nation, 
potion, &c. When A comes after it, it has 
a twofold sound ; one clear and acute, as 
in tAi?i, thief, Sec. the other mote obtuse 
and obscure, as in then, there, &c. 
TABBYING, the passing a silk or stuff 
under a calendar, the rolls of which are 
made of iron or copper, variously engraves, 
which, bearing unequally on the stuff, ren- 
ders the surface thereof unequal, so as to 
reflect the rays of light differently, making 
the representation of waves thereon. 
T. ABERNiEMONTANA, in botany, so 
named in memory of James Theodore, sur- 
named Tabernaemontanus, from BergZap 
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