112 DESCRIPTION OF A LAMfi 



cylinder which fupports it on its (crew, which has nine thready 

 by which means the true fituation to produce the belt effect is 

 obtained, whatever may be the difference of fize between one 

 glafs and another. The fcrews are pewter, but the reporters 

 obferve, that it may be better to make one of them iron. 



et The advantages of railing the oil by a pump moved by a 

 fpring are real, and prevent the wick from becoming charred 

 for want of a conftant fupply of oil ; belides which, as the flame 

 is kept at a diftaneefrom the focket, it can neither calcine the 

 metal nor depofit that cruft of hardened oil which fo foon alters 

 the effects of other lamps. 



The Commilfaries exprefs their approbation of the expedi- 

 ent by which the oil is prevented from leaking through and 

 arriving at the mechanifm, and ftate, that they examined the 

 mechanifm, which they find to be well calculated to produce 

 the defired effecl, and to prove as durable as could be wifhed. 

 Illumination The brilliancy of effed is fpoken of in high terms of appro- 



judged by read- b a tioii. They found that when a white gauze fliade was put 

 mg a book. J p» 'T ^ . * 



over the lamp, they could read m the Ariackarfis or Didot at 



thedifiance of 78 decimeters, or about 24 feet; and that they 

 could read in the fame book at the diftance of 89 decimeters 

 with the flame uncovered. They do not mention the type of 

 the book. 

 Blue chimney. With a chimney of blue glafs they could read at 72 deci- 

 meters. 



When a ground glafs was placed before the flame, they 



could read at the diftance of lb decimeters. A candle placed 



behind the fame glafs, gave a light by which it was difficult to 



read at 23 decimeters. 



Particular de- In addition to the report of the Commiflion of the InfKtute, 



fcription of the t ne Editor of Les Annale»des Arts gives a more minute de- 



thc lamp, fcription, with an accurate engraving, which is prefented to 



the reader in plate IX. 



Fig. 1. View of the under part of the movement of the 

 lamp : aa the lower plate of brafs, which, with the fuperior 

 plate connected by four brafs pillars, forms the frame of the 

 movement : b, ratchet wheel for winding or fctting up the 

 fpring: It is pinned upon the fquare of the barrel arbor, and is 

 kept in its place by the click and back fpring c : The two 

 holes in the face of the wheel are intended to receive the 

 points of a key for winding it up : d, a plate which receives 



the 



