Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 5, BUR-CHI

CAN [ 126 ] CAN
Candle. {We of tallow. Lord Bacon pronofes candles of divers fiderable accuracy are defcribed in the Traitf d'Optique
' compofitions and ingredients, as alfo of different forts of of Bouguer, of which an abridged account is given by
wicks : with experiments of the degrees of duration. Dr Prieilley m his Optics 1 he firft of thefe two me.
and light of each. Good houfewives bury their candles thods has been ufed by others fince that time, and pro¬
in flour or bran, which it is faid increafes their lading bably, before, from its very obvious nature, but parti-
Sdmofl half. cularly by Count Rumford, who has given a deicrip*
tion and drawings of an inflrument called the photome*
Experiments to determine the real and comparative value ter, in the Philofophical Tranfadions for 1794. The
Catvllc*.
of burning CANDLES of different forts and fixes.
Numb.of
candles
in one
pound.
Small wick.
.Large wick.
18^
J9
16^
12
I0|:
71
8
5!
Mould-
candles.
5-ir
4
Weight
of one
candle.
The time
one can¬
dle lafted.
Oz. Dr.
Hr. Min.
14
134
i54-
5t
8
1
o
*3
12
o
The time
that one
pound
will laft.
Hr. Min.
15
40
40
27
36
9
*9
20
3
59
5°
44
41
38
32
34
30
26
34
2
24
24
12
o
15
42
The expence
z hours
when candles
are at 6d per
dozen, which
alfo fliows the
proportion of
the expence
at any price
per dozeip
Farthings and
rooth parts.
4- 85
5- 7°
6- 54
6.96
7- 5°
8.94
8.47
9-53
Mould-candl.
at 7s per doz.
7.87
9.28
N. B. The time that one candle laded was taken
from an average of feveral trials in each frze.
It is obfervable, in optics, that the^ flame of two
candles joined, gives a much dronger light than both
of them feparate.1 The obfervation was fuggeded by
Dr Franklin. Probably the union of the two flames
produces a greater degree of heat, whereby the vapour
is attenuated, and the.particles of which light confids
are more copioufly emitted. 4
Mr Nicholfon has made fome mteredmg obferva-
tions on the light afforded by lamps and candles,
which we (hall lay before our readers in his own
* Philo/oph. words *. “We are acquainted wdh ho means, (fays
J'owr. vol i. unlefs we may except eledtricity, of producing
light but by conlbudion, and this is mod probably of
the fame nature. The rude method of illumination
confids in fuccedively burning certain maffes of fuel
in the folid date. Common fires anfwer this pur-
pofe in the apartments of houies, and in fome hght-
houfes : fmall pieces of refmous wood,, and the bi¬
tuminous coal called Unnel-coal, are m fome coun¬
tries applied to the fame ufe but the mod genera
and ufeful method is that m which fat oil, of an animal
or vegetable kind, is burned, by means of a wick.
Thefe inftruments of illumination are either lamps or
candles In the lamp, the oil mud be one of tho e
which retains its fluidity in the ordinary temperature
the atmofphere. The candle is formed of an oil, or
ether material, which is not fufible but at a tempera¬
ture confiderably elevated. . . _ .
“The method of meafunng the comparative mtenfities
ef light is one of the fird requifites in an inquiry con¬
cerning the art of illumination. Two .methods of con-
principle it is grounded upon is, that if two lights
fhine upon the fame furface at equal obliquities, and
an opake body be interpofed, the two fhadows it will
produce mud differ in blacknefs or intenlity in the
fame degree. For the fhadow formed by intercepting
the greater light will be illuminated by the fmaller
light only, and reverfely the other fhadow will be il¬
luminated by the greater light. That is to fay, irt
fhort, the dronger light will be attended with a deeper
fhadow. But it is eafy, by removing the greater light
to a greater didance, to render the illumination it pro¬
duces at the common furface equal to that afforded by
the lefs. Experiments of this kind may be convenient-
ly made by fadening a fheet of white paper againft
the wall of a room. 1 he two lights or candles intend¬
ed to be compared, mud then be placed fo that the
ray of light from each fliall fall with nearly the fame
angle of incidence upon the middle of the paper. By
fome experiments made in this way in the. year 1785*
I was fatisfied that the degree of illumination could be
thus afeertamed to the Both or 90th part of the wholes
“ By experiments of this kind many ufeful particulars
may be fhewn. Thus, for example, the light of a
candle, which is fo exceedingly brilliant when firft
fnuffed, is very fpeedily diminifhed to one-half, and is
ufually not more than one-fifth or one-fixt.h before the
uneafinefs of the eye induces us to fhuff it. Whence
it follows, that if candles could be made, fo as not to
require fnuffing, the average quantity of light afforded
by the fame quantity of combudible matter would be
more than doubled.* In the fame way, likewife, finc6
the cod and duration of candles, and the Confumption
of oil in lamps, are eafily afcertainable, it may be
fhewn whether more or lefs of light is obtained at the
fame expence during a given time, by burning a num¬
ber of fmall candles indead of one of greater thicknefs.
From a few experiments already made but of the nu¬
merous and ufeful feries that prefents itfelf, I have rea-
fon to think that there is very much wade in this ex-
penfive article of accommodation.
“ In the lamp there are three articles which demand
our attention, the oil, the wick, and the fupply.of air.
It is required that the oil flrould be readily inflam¬
mable, without containing any fetid fubdance which may
prove offenfive, or mucilage, or other matter, to ob-
drua; the channels of the wick. I do not know of any
procefs for ameliorating oils for this purpofe, excepting
that of wafhing with water containing acid or alkali.
Either of thefe is faid to render the mucilage of animal
oils more foluble in the water ; but acid is preferred,
becaufe it is lefs difpofed to combine with the oil itfelf.
The office of the wick appears to be chiefly, if not fole-
ly, to convey the oil by capillary attra&ion to the
place of combudion. As the oil is confumed and flies
off, other oil fucceeds, and in this way a continued
current of oil and maint enance of the flame are effect¬
ed. But as (he wicks of lamps are commonly formed
of