VAR 
form of rain or dew, but above which no 
such diminution could take place with che- 
mical agency. This point may be called 
the extreme temperature of vapour of that 
density ; and That whenever any body 
colder than the extreme temperature of the 
existing vapour is situated in tlie atmos- 
phere, dew is deposited upon it, the quan- 
tity of which varies as the surface of the 
body, and the degree of cold below the ex- 
treme temperature. I'he reader may be 
referred to an excellent and elaborate arti- 
cle on this subject in Dr. Rees’ New Cy- 
clopedia, a work, of which it may be fairly 
and honourably said, that, as it advances in 
its progress, it increases in merit and repu- 
tation, 
VARIABLE quantities, in geometry and 
analytics, denote such as are either continu- 
ally increasing or diminishing ; in opposition 
to those which are constant, remaining al- 
ways the same. Thus, tlie abscisses and or- 
dinates of an ellipsis, or other curve line, 
are variable quantities, because they vary 
or change their magnitudes together. Some 
quantities may be variable by themselves 
alone, while fliose connected with them 
are constant : as the abscisses of a parallelo- 
gram, whose ordinates may be considered 
as all equal, and therefore constant. The 
diameter of a circle, and the parameter of 
a conic section are constant, while their ab- 
scisses are variable. Variable quantities, 
(see Fluxions), are usually denoted by the 
last letters of the alphabet z, y, x, while the 
constant ones are denoted by the first let- 
ters a, b, c. 
VARIANCE, in law, signifies any alter- 
ation of a thing formerly Ibid in a plea, or 
where the declaration in a cause differs 
from the writ, or from the deed upon 
which it is grounded. If there be a vari- 
ance between the declaration and the writ, 
it is error, and the writ shall abate ; and if 
there appear to be a material variance be- 
tween the matter pleaded and the manner 
of pleading it, this is not a good plea, for 
the manner and matter of pleading ought 
to agree in substance, or there will be no 
certainty in it. Cro. Jac. 479. 
VARIATION of curvature, in geome- 
try, is used for that inequality or change, 
which happens in the curvature of all curves 
except the circle ; and this variation, or in- 
equality, constitutes the quality of the cur- 
vature of any line. Sir Isaac Newton makes 
the index of the inequality or variation of 
curvature to be the ratio of the fluxion of 
the radius of curvature to the fluxion of the 
VAR 
curve; and Mr. Maclaurin, to avoid the 
perplexity that different notions, connected 
with the same terras, occasion to learners, 
has adapted the same definition ; but he 
suggests, that this ratio gives rather the va- 
riation of the ray of curvature, and that it 
might have been proper to have measured 
the variation of curvature, rather by the 
ratio of the fluxion of curvature itself to the 
fluxion of the curve ; so that the curvature 
being inversely as the radius of the curva- 
ture, and consequently its fluxion as the 
fluxion of the radius itself directly, and the 
square of the radius inversely, its variation 
would have been directly as the measure of 
it, according to Sir Isaac’s definition, and 
ipversely, as the square of the radius of cur- 
vature. 
Variation of the needle, in magnetism. 
Although the north pole of the magnet in 
every part of the world, when suspended, 
pioints towards the northern parts, and the 
south pole to the southern parts, yet it sel- 
dom points exactly north and south. Th^ 
angle, in which it deviates from due north 
and south, is called “ The vaiiation of the 
needle,” or, “ The variation of tlie com- 
pass,” and this variation is said to be east 
or west, according as the north pole of the 
needle is eastward or westward of the meri- 
dian of the place. This deviation from the 
meridian is not the same in all parts of the 
world, but is difierent in different places, 
and it is almost perpetually varying in the 
same place. When the variation was first 
observed, the north pole of the magnetic 
needle declined eastward of the meridian 
of London, but it has since that time been 
changing towards the west ; so that in the 
year 1657, the needle pointed due north 
and south : at present, it declines towards 
the west between 24° and 2.5°, and it seems 
to be still advancing westward. 
VARIEGATION, among botanists and 
florists, the act of streaking or diversifying 
the leaves, Sec. of plants and flowers with 
several colours. Variegation is either natural 
or artificial. Of natural variegation there 
are four kinds ; the first showing itself in 
yellow spots here and there, in the leaves 
of plants, called by gardeners the yellow 
bloach. The second kind, called the white 
bloach, marks the leaves with a great num- 
ber of white spots, or stripes ; the whitest 
lying next the surface of the leaves, usually 
accompanied with other marks of a green- 
ish white, that lie deeper in the body of 
the leaves. The third, and most beautiful, 
is where the leaves are edged with white, 
