Bauhaus-Universität Weimar

Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine
Gage, Henry Simon and Henry Phelps Gage
papers. If the lamp is kept perfectly dean, and no oil is allowed to 
remain on the outside, the disagreeable smell of partly oxidized oil 
will be avoided. 
§ 199. Amount of oil used.—It takes about half a liter (one 
pint) of kerosene per hour for the best lamps. 
§ 200. Candle-power and size of screen.—The candle-power of 
the best petroleum lamps is not much above ioo. While the older 
lantemists used large screens (4 meters, 12 ft. square) it is better 
to use, with this light, screens of small size, 2 to 3 meters square 
(6-9 ft.), and to keep in mind the requirements for good images 
with these feeble lights (§ 193). 
§ 201. Relative position of lamp and condenser.—In general, 
the middle of the flame should be in the axis of the condenser and 
it should be at about the principal focal distance of the first ele¬ 
ment of the condenser from it (fig. 64). One must get the best 
possible position at any one time by experiment, i. e., by moving 
the light a little closer or farther away than the focus of the con¬ 
denser. For the two-lens condenser the lamp must be closer than 
for the three-lens condenser (§ 17, 55). 
§ 202. The management of an exhibition is as described in 
Chapter I, § 21-41, and above, § 193-194. 
Magic Lantern with a Mantle Gas Lamp 
§ 203. Gas and gas lamps.—The illuminating gas may be 
drawn from the house lighting supply. 
The lamps are of two kinds, the vertical and the inverted or 
reflex form (fig. 68-69). The burner is of the Bunsen type. It 
heats the mantle to incandescence. While there is a very brilliant 
light and a great deal of it, the source is very large, and cannot be 
utilized so completely as the small source of the electric arc lamp 
(see fig. i, 64). 
§ 204. Position of the incandescent mantle.—As this is the 
source of illumination, the middle of the face next the condenser 
should be on the horizontal axis (fig. 64).


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