Proportion of Light from combultible Bodies. [Sup. 
54° 
Quantity Quantity required 
‘Diftance. Intenfity.|contumed | for equal intenfi- 



per hour. ties. 
Oil of poppy feed 10 ee 28 ene | 
3 : 3S 
Argand lamps with }— of fithes 10 10.000 | 23-77 23-77 
_ (C-—-- of cole-feed g.246 | 8.549] 24.18 16.59 
. (Oil of cole-feed 6.774 | 4-588} 8.81 19.2 
€ommon lamps with 4 —- of fithes 6.524 As586.\' Out& t= Zesam 
—- of poppy feed 5.917 2.801 | 274015. ii eels 
Spermaceti candle eae, BUR OR GG ak 26.37 
Old tallow candle 6473 2.O0 Gi. ame 2 cud 
New ditto 5-473 23995 8.23 27.48 
Wax candle A275 82 9.54°1 ) hs 
The relative quantity of combuftible matter required to produce equal lights at 
equal diffances, may be obtained by a fimple rule of propertion from the above 
data. Thus, ifa given intenfity of light, expreffed by 3.501, has been produced by 
a confumption of 9.23 of f{permaceti in the heur, the fame luminous: body will pro- 
duce a light of 10.000, by confuming in the fame time a quantity of fpermaceti 
10.000 X 9.22 
a TO 000 X 9:7 2 —>6.37.—Therefore we may add to the table a fourth column, ex- 
2h OL a) 
preffling the quantity of combuftible which each body muft confume to-produce a 
light of 10.000. 
From what has been laid down, it will alfo appear that the 
number of lights required te 
produce a given light, will be as follows : To produce a light equal to 100 Argand lamps, 
burning poppy-feed oil, ir will require 
too Argand lamps with fifh oil 
117 Ditto 
do. 
219 Ditto with fith oil 
285 Ditto 
Mr. If. next takes notice of the compa- 
rative price of thefe articles, by which he 
finds, that in Paris the mo& expenfive light 
is that produced from wax candies; and the 
moft economical, that from oil of cole-feed, 
burned in Argand lanips.- 
The chief difference between the Ar- 
and and common lamp is, that in the lat- 
ter much of the ot! 1s volatilized without 
combultion, and hence the unpleafant 
fmell which it produces; whereas in the 
former, the heat is $0 great at the top of 
the wick, that all the oil is decompofed in 
patiing through, the difpofition of the 
—4awick allowing the free accefs of air to 
aflift combuftion. et faould therefore 
follow, that the Argand lamp confumes 
iefg fucl to produce a given light than the 
common lamp, and this is the opinion of 
Count Rumford. Yet (Mr. H. obferves ) 
there are two circumftances that prevent 
the ful! effect of the cemplete combuition 
do. sith cole-feed oil 
218 Common lamps with cole-feed oil 
s Spermaceti candles 
3 Tallow ditto 
6 Wax ditto 
1 
do. with poppy-feed oil. 
inthe Argand lamp. The one is, that 
the glafs cylinder abforbs a part of the rays 
of light as they pafs through ; the other, 
that the column of light proceding from 
the inner furface of the wick, Is, in part, 
loft, by being obliged to pals through that 
from the outer furface. Count Rumford 
allows the firft caufe of diminution of 
light, and eflimates it at .1854, but not the 
latter. The author of this memoir, in re- 
peating Count’s R’s experiments, afferts, 
that when two candles are placed fo that 
the light of the one is obliged to pafs 
throught that of the other, the fum of the 
light fo produced, is not fo ftrong 4s when 
they are placed fide by fide ; for in the 
firf cafe, a part of the bindmoft light is 
abforbed by the foremoft. Mr. H. con- 
cludes the paper by fome general obferva- 
tions on the comparative elegance and’ uti- 
lity of the various methods of illumination. 
For 
