OP THE MICftOSCOPE. 217 



LAMP. Any lamp, or even candle, will answer, but we prefer 

 a spirit lamp, the flame being free from smoke and easily man- 

 aged. At night the kerosene lamp used for giving light will 

 answer. Where gas is used, the Bunsen burner is a great con- 

 venience. Whatever lamp or burner be used, it should be sur- 

 rounded with a chimney or shade, so as to prevent the flicker- 

 ing of the flame by currents of air. The best shade is a tin 

 cylinder, with rows of holes at top and bottom for the admis- 

 sion and exit of air. 



RETORT STAND. .. suitable retort stand is a very simple 

 affair, and is best made at home. Ours consists of a board of 

 hard wood, 5 inches by 4, into which is screwed a rod fourteen 

 inches long, and a quarter of an inch in diameter. The rings 

 have no screws, but are simply pieces of wire, one end of which 

 is twisted round the rod, while the other is formed into a ring 

 of the required size. Kings formed in this way are easily 

 moved on the upright rod, but no weight placed on them in 

 the usual manner can cause them to slip down. 



CARDS FOK CENTERING THE OBJECTS. Unless the objects 

 are placed on the centres of the slides, the latter have a very 

 awkward look. By drawing the outlines of a slide on a card, 

 and marking out the centre, this difficulty is easily overcome. 

 A card marked off in this way is shown in Fig. 69. 



Fig. fi9. 



It is well to have two cards, one black with a white centre, 

 and the other white with a black centre, as some objects, when 

 immersed in the medium in which they are to be mounted, 



