Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 6, CHI-Crystallization

C H R [ 74 ] C H R
f.hrifto-
pher’s
i!
Chromatic.
light, fandy, and fruitful j but the ifland is fubjeft to
hurricanes. The produce is chiefly fugar, cotton, gin¬
ger, indigo, and the tropical fruits. W. Long. 62. 32.
N. Lat. 17. 30.
CHRO AST ACES, an old term in Natural Hi/lory,
applied to gems, and comprehending all thofe of vari¬
able colours, as viewed in different lights and in dif¬
ferent pofitions y of which kinds are the opal and the
ajleria or cat’s eye.
CHROMATIC, a kind of mufic which proceeds
by feveral femitones in fucceflion. The wqrd is de¬
rived from the Greek wupx,, which fignifies colour.
For this denomination 1’everal caufes are afligned, of
which none appear certain, and all equally unfatisfac-
tory. Inftead, therefore, of fixing upon any, we flrall
offer a conjedture of our own ; which, however, we
do not impofe upon the reader as more worthy of his
attention than any of the former. X^upct, may per¬
haps not only fignify a colour, but that of a (hade of a
colour by which it melts into another, or what the
French call nuance. If this interpretation be admitted,
it will be highly applicable to femitones j which being
the fmalleft interval allowed in the diatonic fcale, will
mofl: eafily run one into another. To find the reafons
affigned by the ancients for this denomination, and
their various divifions of the chromatic fpecies, the
reader may have recourfe to the fame article in Rouf-
feau’s Mufical Didlionary. At prefent, that fpecies
confifls in giving fuch a procedure to the fundamental
bafs, that the parts in the harmony, or at leaf! fome
of them, may proceed by femitones, as well in riling
as defcending •, which is moll frequently found in the
minor mode, from the alterations to which the lixth and
feventh note are fubjedled, by the nature of the mode
itfelf.
The fucceffive femitones ufed in the chromatic fpe¬
cies are rarely of the fame kind ; but alternately ma¬
jor and minor, that is to fay, chromatic and diatonic:
for the interval of a minor tone contains a minor or
chromatic femitone, and another which is major or dia¬
tonic ; a meafure which temperament renders common
to all tones : fo that we cannot proceed by two minor
femitones which are conjun&ive in fucceflion, without
entering into the enharmonic fpecies $ but two major Chromatic,
femitones twice follow each other in the chromatic or- v—J
der of the fcale.
The mofl: certain procedure of the fundamental bafs
to generate the chromatic elements in afcent, is alter¬
nately to defcend by thirds, and rife by fourths, whilft
all the chords carry the third major. If the funda¬
mental bafs proceeds from dominant to dominant by
perfect cadences avoided, it produces the chromatic in
defcending. To produce both at once, you interweave
the perfect and broken cadences, but at the fame time
avoid them.
As at every note in the chromatic fpecies one mull
change the tone, that fucceflion ought to be regulated
and limited for fear of deviation. For this purpofe, it
will be proper to recoiled!, that the fpace moft luitable
to chromatic movements, is between the extremes of the
dominant and the tonic in afcending, and between the
tonic and the dominant in defcending. In the major
mode, one may alfo chromatically delcend from the do¬
minant upon the fecond note. This tranfition is very
common in Italy ; and, notwithftanding its beauty, be¬
gins to be a little too common amongft us.
The chromatic fpecies is admirably fitted to exprefs
grief and affliction ; thefe f unds boldly ftruck in af¬
cending tear the foul. Their power is no lefs magi¬
cal in defcending \ it is then that the ear feems to be
pierced with real groans. Attended with its proper
harmony, this fpecies appears proper to exprefs every
thing j but its completion, by concealing the melody,
facrifices a part of its expreffion j and for this dif-
advantage, arifing from the fulnefs of the harmony,
it can only be compenfated by the nature and ge¬
nius of the movement. We may add, that in propor¬
tion to the energy of this fpecies, the compofer ought
to ufe it with greater caution and parfimony ; like
thofe elegant viands, which, when profufely admini-
ftered, immediately forfeit us with their abundance }
as much as they delight us when enjoyed with temper¬
ance, fo much do they difguft when devoured with pro¬
digality.
Chromatic, Enharmonic. See Enharmonic.
CHROMATICS;
rT ’HAT part of optics which explains the feveral
properties of the colours of light, and of natural
t bodies.
Different Before the time of Sir Ifaac Newton, we find no
hypothefes hvpothefis concerning colours of any confequence.
cencerning opinions of the old philofophers, however, we
colours. briefly mention, in order to gratify the curiofity
of our readers. The Pythagoreans called colour the
fuperfices of body. Plato faid that it was a flame if-
fuing from them. According to Zeno, it is the firft
configuration of matter j and Ariftotle faid, it was that
which moved bodies a<flually tranfparent. Des Cartes
afferted, that colour is a modification of light j but he
imagined, that the difference of colour proceeds from
the prevalence of the diredt or rotatory motion of the
particles of light. Father Grimaldi, Dee hales, and
many others, thought the difference of colour depend¬
ed upon the quick or flow vibrations of a certain elaf-
tic medium filling the whole univerfe. Rohault ima¬
gined that the different colours were made by the
rays of light entering the eye at different angles with
refpedt to the optic axis; and from the phenomena of
the rainbow, he pretended to calculate the precife
quantity of the angle that conftituted each particular
colour. Laftly, Dr Hooke, the rival of Newton, ima¬
gined that colour is caufed by the fenfaiion of the ob¬
lique or uneven pulfe of light $ and this being capable
of no more than two varieties, he concluded there could
be no mere than two primary colours. 2
In the year 1666, Sir Ifaac Newton began to invef-This fub-
tigate this fubjedt j and finding the coloured image ofie<^ inveH
the fun, formed by a glafs prifm, to be of an oblong,
and Newton.