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cannot by the fight be diftinguifhed from the denfe opake 
metals; and this fimilarity to the furface of metals not 
only occurs, when from the roughnefs of their furfaces 
they refemble polifhed metals in whitenefs, but alfo when 
from their fmoothnefs they refemble the polithed furface 
of metals. 
It thould feem, that metals confift entirely of tranfpa- 
rent matter, and derive their apparent opacity and luftre 
iolely from the copious reflection of light from their fur- 
faces. The analogy between metals and tranfparent me¬ 
dia, as far as concerns,their optical properties, will appear 
plain from the following confiderations : i. All metals 
dillblved in their proper menftrua are tranfparent. 2. By 
the union of two or more tranfparent media, fubftances 
are conltiruted which are fimiiar to metals in their opa¬ 
city and luitre, as plumbago and marcafites. 3. The tranf¬ 
parent fubftances of metals, as well as thofe of minerals, 
by their union with inflammable matter, acquire the ftrong 
refieCtive powers from which their luftre and opacity arife. 
4. The furfaces of pellucid media, fuch as glafs or water, 
aflfume a metallic appearance, when by their fmoothnefs, 
difference of denfity with refpeCt to the contiguous me¬ 
dia, or any other, they are difpofed copioufly to reflect 
the light. 
It is plain from the foregoing confiderations, that opake 
fubftances are conftituted by the union or contiguity of 
tranfparent colourlefs media, differing from one another 
in their refleCtive powers; and that when the common 
furface, which comes between fuch media, is plane, equal, 
and fmooth, it reflects the incident rays equally and re¬ 
gularly as a mirror; but when their furface is rough and 
unequal, or divided into minute particles, it reflects the 
incident rays irregularly and promifcuoufly in different 
directions, and eonfequently appears white. When the 
interftitial vacuities of bodies are fo.difpofed that the light 
can preferve its rectilinear courfe through them, fuch bo¬ 
dies appear luminous throughout, and are vifible in their 
internal fubftance; but when their conftitution is fuch as 
will not allow a free paffage to the light, they are then vi- 
ftble only by thofe rays which are reflected from their fur¬ 
face, and their internal furface is cold and dark. 
Sir Il'aac Newton found, on comparing the refraCtive 
power of different bodies, that inflammable fubftances 
poffefs it in a much greater degree than fuch as are not 
inflammable. From his obfervations on this fubjeCt, he 
drew the wonderful conclulion, that the diamond con¬ 
tained a large quantity of inflammable matter; that water 
was an intermediate fubftance between inflammable and 
unimflammable bodies, and that it fupplied vegetables 
■with the inflammable principle ; which truths have been 
leen and demonftrated only in our own time. Subftances 
that are not tranfparent in their ordinary ftate, may be 
rendered fo either by relaxing their parts with heat, fo that 
the light may pafs through them more eafily, or by giving 
fome new direClicn, together with an additional force, to 
the matter of light. Mr. Hawklbee was very much fur- 
prifed to find, that the fealing-wax, and the pitch, within 
fide a glafs globe, became fo transparent when the glafs 
was whirled about and rubbed with the hand, that the 
fingers might be plainly feen on'the other fide through the 
coating. Oil is condenfed, when cold, into a fort of 
globules impervious to the light; but when thefe globules 
are dilfolved, and opened by the aCtion of caloric, the oil 
not only becomes tranfparent, but appears as bright and 
fhining as if the light were a natural part of its compofi- 
tion. We know, that many heterogeneous fluids grow 
dark and muddy with cold, but that they may be foon 
clarified again by the application of a moderate heat: red 
poit wine is fometimes as foul as if brick-dull was mixed 
with it, but will become bright and clear by the applica¬ 
tion of warmth. 
Transparency is a quality given, by a wife ordination 
of Providence, to the fluid fubftance of water, which is fo 
neceflary to the life of all animals. Tranfparency renders 
glafs molt valuable 5 the value of gold is arbitrary, but 
C H R 531 
the worth of glafs is intrinfic; its cleanlinefs and tranf' 
parency recommend it to our ufe in the common arts 
life; and, render vifible the raoft curious and fubtil pro - 
cefles of chemiftry and philofophy: in optics, it afllits th e 
aged, and gives to man an infight into the wonders of.the 
creation.—For the lateft mathematical inveftigation of th e 
doftrine of light and colours ; the method of producing 
the artificial rainbow; and many other entertaining and 
curious experiments, lee the article Optics. 
CHRO'MATISM, f. Gr.] The natural 
colour or tinfture of any fubftance. With ph\ficians, 
it is the morbid difcolouration of the blood and animal 
juices. 
CHRONHYO'METER, f. The time-rain gauge, in¬ 
vented by Landrianus. 
CHRO'NIC, or Chro'nical, adj. [from time.] 
A term implying-duration or continuance. In medicine, 
chronic dillempers are oppofed to acute.—Of difeafes fome 
are chronical, and of long duration; as dropfies, quartan 
agues, fcurvy, wherein we defer the cure unto more ad¬ 
vantageous leafons. Broswn. —See the article Medicine. 
CHRO'NICLE,/. [ chronique , Fr. from xqovoc, Gr. time.] 
A regilter or account of events in theorder of time : 
No more of this ; 
For ’tis a chronicle of day by day. Shakefpeare. 
A hiftory.—I give up to hiftorians the generals and he^ 
roes which crowd their annals, together with thofe which 
you are to produce for the Britilh chronicle. Dryden, 
To CHRO'NICLE, no. a. To record in chronicle, or 
hiftory.—This to rehearfe, fiiould rather be to chronicle 
times, than to fearch into reformation of abules in Ire¬ 
land. Spenfer. —To regilter; to record .- 
Love is your mailer, for he mailers you; 
And he that is fo yoked by a fool, 
Methinks fhould not be chronicled for wife. Shakefpeare. 
CHRO'NICLER,/ A writer of chronicles; a recorder 
of events in order of time : 
Here gathering chroniclers, and by them Hand 
Giddy fantaftic poets of each land. Donne. 
An hiltorian ; one that keeps up the memory of things 
pall.—This cultom was held by the druids and bards of 
our ancient Britons, and of latter times by the Irifli 
chroniclers, called rimers. Raleigh. 
CHRO'NOGRAM,/ [p^ovoc, time,and yeutpa, to write.] 
An infeription bearing the date of any abtion. Of this 
kind the following is an example : 
Gloria laufque Deo fteCLorTM in faecFla funto. 
A chronogrammatical verfe, which includes not only this 
year, but numerical letters enough to reach above a thou- 
land vears further. Ho-zvell. 
CHRONOGRAMMATICAL, adj. Belonging to a 
chronogram. 
CHRONOGRAM'MATIST, y. A writer of chrono¬ 
grams.—There are foreign univerfities, where, as you 
praife a man in England for being an excellent philofo- 
pher or poet, it is an ordinary chara&er to be a great 
chronogrammatijl. Addifon. 
CHBONO'LOGER, /. time, and A070$, doc¬ 
trine.] He that ltudies or explains the fcience of com¬ 
puting pall time, or of ranging pail events according to 
their proper years.— Chronologers differ among themfeives 
about moil great epochas. Holder. 
CHRONOLO'GICAL, adj. Relating to the doftrine of 
time.—Thus much touching the chronological account of 
fome times and things pall, without confining myfelf to 
the exailnefs of years. Hale. 
CHRONOLO'GICALLY, qdv. In a chronological 
manner; according to the laws or rules of chronology; 
according to the exact feries of time. 
CHRONO'LOGIST, J'. One that ltudies or explains 
time ; one that ranges pail events according to the order 
of 
