THE RAD 



give such a disc with modern phoi 



are still used to some extent, on accoul 



freedom from risk of fire. Only such 



lanterns for the navy ; and they are usefuf 



where things become dry like tinder. Some 



can also be generally obtained when nothing else 



hence these lamps are sent out to missionaries. 



Such lamps are of two kinds : viz. with the cistern 

 beneath, as part of the lamp, and with a separate cistern ; 

 but the wick arrangement is, with little modification, similar 

 in both. This is what is known as a ' solarised ' Argand, 

 external and internal metal cones concentrating an upward 

 current of air upon both inside and outside of the wick, so as 

 to give intensity to the light. The oil may be either sperm, 

 or colza, or olive, and greater whiteness and solidity of flame 

 is generally obtained if camphor is dissolved 

 in it. Fluid oil can be used alike in either 

 form of lamp ; but when the cistern is beneath, 

 so as to keep hot while burning, either tallow 

 or solid paraffin will also burn excellently if 

 first melted. The last solid paraffin so 

 melted I think gives the best light of all, but 

 it may not burn equally well in all lamps. 

 Such solid fatty matter cannot of course be 

 used in cistern lamps, like fig. 22, which are 

 now most usual. The glass chimneys of these 

 lamps must be pretty tall, and are tapered 

 towards the top. 



There is little difficulty in getting a light of about twenty- 

 eight candles with these lamps ; and as the flame is trans 

 parent, this can be increased to about thirty-five candles by 

 using a reflector, which is always done. This must not be 

 parabolic, but circular, the centre of curvature being the flame 

 itself ; the rays are then reflected back in the same path, and 

 go to the condenser just as if emitted by the radiant. The 



D2 



FIG. 22 



