LANTERNS AND THEIR MANIPULATION 115 



and the condensers replaced when they have been removed 

 for warming. If bags are used they will be weighted, and 

 the tap of the hydrogen bag or cylinder turned on ; where gas 

 from the main is used it will be already on at the dissolver. 

 The latter being turned on to both lanterns, limes will be 

 placed on the pins, first clearing their holes, and wiping off 

 all loose powder with a bit of paper ; and the nipples of the 

 jets will be adjusted to the known distance if needful. 

 Turning each hydrogen tap half on in succession, the jets 

 will be lighted, and the flame turned down moderately, when 

 the limes will be turned round and warmed. When well 

 heated throughout, one lantern will be turned off by the 

 dissolver, and the ' on ' lantern have its jet adjusted for bright- 

 ness according to the details in Chapter IV. The next step is 

 a very important one. 



JKJ. 64. Adjustment of the Light 



62. Adjustment of the Light. The lime has now to be 

 got into the position which gives a disc evenly illuminated all 

 over. This can only be properly done in one way. Any slide 



i2 



