Ch. IX] DO AND DO NOT IN MICRO-PROJECTION 
16. Use a hood on the objec¬ 
tive to aid in centering the light 
and in placing the objective the 
right distance from the conden¬ 
ser (§ 372); a light shield 
beyond the objective to stop 
stray light is also an advantage 
(§ 373)- 
17. It is of the utmost im¬ 
portance that every part be 
accurately centered for micro¬ 
projection (§375), and that the 
parts should be separated from 
one another the right distance 
(§ 376, 382). 
18. Remember that it is a 
pure waste to use too great an 
amperage (§ 378). 
19. As the same object is to 
be shown entire and with magni¬ 
fied details and different objects 
require different magnifications, 
it is convenient to have two, 
three or four objectives of 
different powers in a revolving 
nose-piece (§ 379). 
20. For exhibition purposes 
it is a great advantage to use 
carbons whose ends have been 
shaped by previous burning in 
the lamp (§ 380). 
315 
16. Do not forget the advan¬ 
tages of an objective hood for 
centering the light and prevent¬ 
ing glare; and do not omit the 
light shield to cut off stray light. 
17. Do not fail to have all 
parts accurately centered, and 
the correct distance apart. 
18. Do not use a greater cur¬ 
rent than necessary. 
19. Do not show all objects 
with the same objective, but 
have two or three on a revolving 
nose-piece so that different 
powers can be used with the 
minimum of trouble. 
20. Do not forget to shape 
the ends of the carbons by burn¬ 
ing them awhile in the arc lamp 
before any formal exhibition.