Vor. IV.] Proportion of Light from combuftible Bodies, 
Thirty guilders is the difference for 
every fhilling Flemith for rool. fterling, 
‘and for every half-groot one guilder five 
ftivers. es 
The exchange, at 35s. a groot, more 
vor lefs, is 4s. gd. in rool. fterling ; at 
36s.—4s. 74; ‘at 378.—4s. 6d at 35s. 
—4S. 43 5 398.—4s. 3d; and, at gos. ex- 
adtly 4s. 2d. é 
The courfe of exchange being affect 
ed both by the neceffity for making com- 
mercial remittances and the negociation of 
bills, it can neither be exprefsly governed 
by the par of the money of the countries 
traded with, nor determine. the balance of 
trade between them. Jt only, at the time 
of payment, decides the cof of each 
country’s imports, and the price of its ex- 
ports ; but, frém numerous artificial caufes, 
can never determine the degree of either. 
That country which generally poffeffes 
the exchange in its favour, may be in- 
duced to import foreign produétions, be- 
caufe of their cheapnefs, while its own ex- 
ports and manufaétures are declining be- 
caufe rendered too dear for foreign con- 
fumption, which often cccafions a very in- 
jurious delay of remittances. 
In Holland, Hamburgh, and all thofe 
countries where the exchange is governed 
by giving pounds Flemith for fterling 
money; the Aigber the exchange, the 
more itis in favour of Great Britain. But 
in Ruffia, France, Spain, Italy, and the 
South of Europe, where their currency is 
negotiated at a certain number of pence 
fterling ; the /owef exchange is the moft 
in favour of this country. 
Norwich, March 14th, 1797: sey 

For the Monibly Magazine. 
MEMOIR ON THE PROPORTIONAL 
QUANTITY OF LIGHT GIVEN BY 
DIFFERENT COMBUSTIBLE BopieEs, 
AND ON THE VARIOUS KINDS oF 
Lamps THAT ARE CGMMONLY 
MADE USE OF. 
By J. H. Hassenrrarfz. 
Annales de Chimie, No. 70. 
6 besa French government employed Mr. 
H. in the year 1795, to make a {eries 
ef experiments, to determine the moft eco- 
nomical method of procuring light from 
the different combutftible fubftances ufually 
employed. Mr. H’s experiments differ 
in fome degree from thofe of Count Rum- 
ford, the caule of which he endeavours to 
explain. The materials of Mr. H.’s ex- 
periments were wax, {permaceti, and ral- 
low candles, fifh-oil, oi! of colefeed, and 
of poppy-feeds. In ufing thefe oils, both 
the Argand and common lamps were em- 
$39 
ployed. The wicks of the latter were 
round, containing thirty-fixcotton threads, 
The tallow and {permaceti candles were 
mould, fix to the pound. The wax can- 
dies five tothe pound. Mr. H. ufed the 
fame method with Count Rumford, for 
determining the comparative intenfity of ~ 
the lights. It confifts in placing the two 
luminous bodies at-different diftances on 
white paper, putting a {mall opaque cylin~ 
der near this paper, and gradually remov- 
ing the light, till the fhadow produced by 
each be of the fame intenfity. The in- 
tenfity of the light is then in proportion te 
the {quares of the diftances of the luminous 
bodies, from the- life of union of their 
two thadows on the white paper. Count 
Rumford ufed the Argand lamp asa 
ftandard for comparifon; but as the inten- 
fity of its light varies according to the 
height of the wick, Mr. H. preferred a 
wax candle, making ufe of it foon after it 
wasjlighted. When two luminous bodies, of 
different intenfities, are put in comparifon 
with each other, the fhadows are of twe 
colours. That from the weakeft light is 
blue, and from the firongeft, red. When 
the Jights of two different combuftible bo- 
dies are compared, they are either red or 
biue in a compound ratio of the colour and 
intenfity.§ Thus in comparing the fha~ 
dows from different luminous bodies, they 
will be red or blue refpeétively, in the fol- 
lowing order : : 
Light of the fun. 
of the moon. 
of Argand lamps. 
of tallow candles, 
- of \wax ditto. 
—-— of fpermaceti ditto. 
——- of common lamps. 
That is to fay, when a body is illus 
minated by the fun and by any other lu- 
minous fubftance, the fhadow of the for- 
mer is red, and of the latter, blue. In 
like manner, the thadow from an Argand 
lamp is red, when placed by that of a tal- 
low candle, which is blue. 
The following table will fhow the pro- - 
portional diftance that different luminous 
bodies fhould be placed to produce an e- 
qually intenfe fhadow from thefame object. 
The fecond column gives the propor- 
tional intenfity of each light, which is 
known to be in proportion to the fquares 
of the diftances of luminous bodies giving 
the fame depth of fhadow. 
The third column fhows the quantity of 
combuftible matter confumed in the hour 
by each mode of giving light, which Mr, 
H. calculates frorn the ayerage of many 
repeated experiments. 
ae me 

Diftance 
