110 DESCRIPTION OF A LAMP. 



chimney not being capable of being made to that degree of 

 accuracy as to afford the contraction always at the fame 

 height, the effect of this contrivance could not be thebeft pof- 

 fible, excepting when the accidental concurrence of circum- 

 flances might render it fo. 



" At the fame time that they were bufied in remedying 

 thofe inconveniences, they did not neglect the means of ren- 

 dering the lamp more economical, convenient, and portable ; 

 without fear of fpilling the oil ; without any confiderable effect 

 upon the flame by motion ; without any interception of the 

 light from a refervoir; and with the addition of an agreeable 

 and ornamental form. 



<e The account refulting from our examination will enable 

 the Clafs tojudge of the difficulties they have had to vanquifh, 

 the ingenious proceffes they have ufed, and the fuccefs which 

 has crowned their induftry. 

 Experiments " The mechanical lamp was lighted before the Clafs for a 



with the new ^^ fime The ^ few the bri j liant light ; t a fr or ded, and com- 

 pared that light with the lamps which ufually illuminate their 

 place of meeting. It continued abfolutely the fame five hours 

 after it had been lighted, thojugh the wick had not been altered 

 or touched. 

 Compared with " In order to determine more exactly the intenfity of the 

 it he iv°eTmore !i S ht ' Jt was P^ced at fuch a diftance that a body interpofed 

 than twice the between its light prodeced a fhadow of the fame obfeurity as 

 light. t j iat () f a common Argand's lamp. The diftances were — 



from the mechanical lamp forty-fix decimeters, and from the 

 common lamp thirty-three decimeters, which, by the fquare of 

 the diftances, gives the ratio of 2116 to 1039, or 100 to 48|, 

 for the intenfities of the light. 



" The common lamps of this conflruction not always afford- 

 ing a light perfectly uniform, and the glafs chimney of that 

 which we employed not being of the moft favourable dimen- 

 fions, we thought it proper to endeavour to obtain a confirma- 

 tion of this ratio by the comparifon with candles, of which the 

 light is lefs fubject to vary. 

 Comparifon with " Six candles (I fuppofe of wax), of the weight of one hec- 

 candles. togram (five to the French pound), were arranged in fuch a 



manner that their flames could not mutually intercept each 

 other. The fhadow produced by the interpofition of an opaque 

 body received on a card, was found to be fimilar to that of the 



mechanical 





