116 LA 
cd. Let the two lamps, or other burning bodies to be 
compared, be denominated A and B ; and let them be 
placed at equal heights upon two light tables, or movea¬ 
ble Hands, in a darkened room ; let a flieet of clean white 
paper be equally fpread out, and fattened upon the wain- 
fcot, or fide of the room, at the fame height from the floor 
as the lights; and let the lights be placed oppofite to this 
flieet of paper, at the dittance of fix and eight feet from 
it, and the fame from each other, in fuch a manner, that 
a line drawn from the centre of the paper, perpendicu¬ 
lar to its furface, (hall bife< 5 t the angle formed by lines 
drawn from the lights to that centre ; in which cafe, 
confidering the paper as a plane fpeculum, the one light 
will be precifely in the line of reflection of the other. 
If the one light be weaker than the other, and the 
■weaker being placed at the dittance of four feet from 
the centre of the paper, it fliould be found neceflary, 
in order that the thadows may be of the fame denfity, 
to remove the ftronger light to the dittance of eight 
feet from that centre; in that cafe, the real intenfitv of 
the ftronger light will be to that of the weaker as 8 2 to 
4*, or as 4 to i. When the fliadows are of equal denfity 
at any given point, the intenfity of the rays at that point 
are alfo equal. The greateft care mutt be taken in every 
cafe that the lights compared be properly trimmed, elle 
the refults of the experiments will be inconclufive. 
Count Rumford found, from a variety of experiments 
conducted with his ufual caution, that, if oil be burnt in 
the lamp called Argand’s lamp inftead of one of the com¬ 
mon conftruftion, the confumer has a clear faving of 15 
per cent, an objeft of attention furely to thofe whole 
finances are circumfcribed. The principal difference be¬ 
tween thefe two lamps is, that in the common lamp much 
of the oil is volatilized, without undergoing that procefs 
of combuftion from which originates the difagreeable 
fmell produced by it ; whereas in Argand’s lamp the heat 
is fo intenfe at the top of the wick, that the oil is decom- 
pofed in its paffage through it, the wick being fo difpofed 
as to admit free accefs to the air, for the purpofe of aiding 
combuftion. 
The count, having made experiments with different 
inflammable fubftances, in order to afcertain which is the 
cheapeft ormoft economical, obtained the following refults. 
229 
129 
125 
120 
Bees-zoax .—A good wax candle, kept well fnufted, *n U wei£h" 3 
and burning with a clear bright flame, - - - 100 
Tallozv .—A good tallow candle, kept well fnuffed, 
and burning with a bright flame, ----- 101 
The fame burning dim for want of fnuffing, - 
Olive-oil —Burnt in an Argand’s lamp, with a clear 
bright flame without fmoke, -----. 
Rape-oil —Burnt in the fame manner, - - - ■ 
Linfeed-oil —Likewife burnt in the fame manner. 
This table, together with the current prices of the ar¬ 
ticles mentioned in it, will enable any perfon to afcertain 
the relative prices of light produced by thefe materials. 
It is worthy of obfervation, that 100 of Argand’s lamps 
burning with fiffi-oil, are equal to 218 common lamps, 
3.85 fpermaceti candles, 333 tallow ditto, or 546 wax can¬ 
dles ; from which it evidently appears, that an Argand’s 
lamp is vaftly fuperior, in point of economy, to any other 
burning body commonly made ufeof by families orin fliops. 
Many improvements have been made, from time to time, 
upon this excellent invention; among which we may no¬ 
tice that of Meflrs. White and Smethurft, in 1800, the ob¬ 
ject of which is to caufe a more free and plentiful fupply 
of oil to the ignited part of the wick, by which means 
it may burn better, require fnuffing lefs frequently, will 
burn with oil of an inferior quality, and the burner may 
be more eafily cleaned. Thefe advantages are obtained 
limply by leaving more fpace between the two tubes within 
which the wick is confined than is ufually done. It is ne- 
ceflary however to reduce to the ufual fize the fpace at 
the top of the wick, in order that the burnt cruft may be 
more conveniently bruffied off. This may be done by 
M 
putting on a ring conically fliaped, fo as to bring the fpace 
at top to the requifite dimenfion. The principle of im¬ 
provement here is to take away the clofe adhefion between 
the fides of the unburnt wick and the tubes between 
which it is confined; for, as this part of the wick is con- 
ftantly foaked in oil, it thereby adheres clofely to the fides 
of the tubes, and the capillary attraction by which the oil 
is drawn up into the burning circle of the wick, is thus 
much lefs than it would be if the wick were limply hang¬ 
ing down loofely to the oil refervcir. At the fame time 
all the important advantage gained by the Argand con- 
ftru6Hon is preferved equally well merely by the ring at 
the top of the wick-tube. The patentees fuggeft other 
methods of con (trusting the fupporters of the wick, as 
for inftance, by fupporting a ring upon pillars or bars, or 
by making flits or openings in the fides of the tubes, and 
the like, all of which will er.fure the fame advantages. 
One of the ttioft important benefits which the patentees 
affert will be derived from their improved lamp, is to 
enable the wick to burn common whale or feed-oils, which 
are fold nearly at half the price of the bell: fpermaceti-oii; 
and it is probable that, if the lamp burns well, little, if 
any, of the offenfive fmell occafioned by thefe oils, when 
burnt in the common way, will be perceived. 
Smet/iurjl's Lamp, 1791. “The end and defign of this 
lamp is, to produce a flrong light, and fo to manage that 
light, that it may be thrown in any required direction. 
But this is not the only advantage and peculiarity in its 
conftruction ; for, while this lamp diffufes a flrong light 
to a great diffance, it does not create or leave any unplea- 
fant ihade or darknefs; light is communicated all round 
from the fore part, the back part, the fides, and the bot¬ 
tom, of the lamp. It confifts of a lamp for one, two, 
three, or four, beveled or Hoped lenfes; the lenfes may 
be plane-convex, double-convex, concave-convex, or of 
unequal convexities. The bevel to the lenfes may be 
ftraight, oblique, concave, or convex, in any direction 
or curve, or of any figure or fliape, with fnany or few an¬ 
gles. One, two, three, or more, fides of the lenfes, may¬ 
be beveled, or any portion of its curvation, circumfer¬ 
ence, and fides. The beveled lenfes may be fixed fo as to 
be immovable, or fo as to be moved in any required di- 
reflion. The lamp and lenfes are made to hang on the 
frame ; or the frame or lamp, or the part containing the 
oil and cotton, may be affixed to the lenfes. The lamp may 
be taken out independent of, or with, the lenfes. The 
lamp, or part containing the oil and cotton, may be made 
of any fliape, form, or pattern; the burners, or piece car¬ 
rying the cotton or wick, may be alfo made of any fliape 
or form; it may be fixed or moveable, Aiding backwards 
or forwards, or remaining in any given pofition, to throw 
or fpread the light in any direftion or pofition ; it may be 
made to hold either a flat, or round, or irregular-fhaped, 
cotton or wick. The burner and lamp may be taken in 
and out with great eafe; they may be taken out and the 
lenfes left behind, or they may be taken out together 
with the lenfes, or ufed without any lenfes at all, if re¬ 
quired. The beveled lenfes may be ufed or applied to ad¬ 
vantage to lamps for lireets, fquares, houfes, halls, flair- 
cafes, paffages, lanes, alleys, or for reading, writing, and 
for all other purpofes where a flrong and diffufed light is 
required. Fig. 1, of the annexed Plate, reprelents a lamp 
or burner, with three beveled lenfes, a, b, c. The bottom, 
and two of the fides, of each of thefe lenfes, are beveled. 
The lamp, d e, is of the fountain kind, and is connected 
by a tube with the part f g, which carries the cotton; the 
burner, or tube, cannot be feen in the drawing, being hid 
by the lens b. h , 2, k, is the frame to which the lamp and 
lenfes are affixed. Fig. 2 reprefents a circular lamp, or 
burner, with two beveled lenfes. This drawing lhows 
the manner in which the lenfes may be fixed, fo as to be 
moveable in various directions. a,b, c, d, the circular part 
of the burner or lamp, e f, the neck, trough, or receiver, 
which carries the wick and oil; this is here reprefented as 
moveable in a groove, or may be fet in different pofitions 
