204 E. M. NELSON ON DARK-GROUND ILLUMINATION. 



description of the lamp, as the plan of the original one, owing 

 to its many "improvements," seems to have been forgotten. 



Descriptioyi of Lamp. The lamp has a paraffin burner with 

 a |-in. wick. The reservoir is broad and shallow, 1 in. deep 

 inside measurement ; shallow in order that the lamp flame may- 

 be brought down close to the table, for which reason the burner 

 should be close to the top of the reservoir ; and broad so that the 

 heat may be dissipated by the large surface. The surface of my 

 lamp cistern has a total area of over 60 square in., which i& 

 equivalent to a cylindrical reservoir of 5*4 in. in diameter, and 

 1 in. deep. A large quantity of heat is conducted to the 

 reservoir by the metal chimney, so lamps with small reservoirs 

 are absolutely dangerous, as the oil may boil. I have seen this 

 occur in an " improved " lamp ; the oil is vaporised and burns 

 with a large flame at the top of the chimney. My lamp is 

 often alight for twelve hours at a stretch, and it has never been 

 known to get hot. Below the reservoir an arm capable of rota- 

 tion is pivoted, the middle of the flame being in the axis. This 

 arm is slotted, and in the slot a tubular post which carries 

 the bull's-eye rod slides freely. This post has a clamping nut 

 at the bottom to fix it. The bull's-eye rod slides up and down 

 in this tube, and can be fixed at any height by a clamping collar. 

 The reservoir with all this attached to it slides up and down 

 a pillar on a firm foot ; it, too, is fixed by a clamping collar. 

 Note, this collar should be above the reservoir and not below it,. 

 in order that it may not be covered with drops of oil. The 

 vertical pillar has a slot cut along its whole length, and the tube 

 to which the reservoir is attached has a pin to fit this slot ; this 

 keeps the lamp over its foot, for if the reservoir swings round to 

 one side of the foot it is more than likely that the whole thing 

 will capsize. The chimney is made of blackened brass, with a 

 window 1^ in. long and 1 in. wide to take a 3 X 1-in. shp, which 

 should be of the thinnest kind. Rack work adjustment to th& 

 lamp is not only useless, but in the way, for the efiect of lamp 



