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On Light.
TO THOSE ABOUT TO BECOME BIOSCOPISTS.
A powerful light is the prime condition in producing the best effect of animated pictures upon the screen. Owing to the scattered radient (or rays) of light derived from oil, acetylene, or spirit burners, their use is very unsuitable for lantern work, and absolutely useless for the cinematograph. The stronger the radient of light, the brighter and sharper the definition of animated pictures.
The various powers obtained from the different sources of light according to photometric tests are : —
4-wick Oil Lamp 80 to 100 c.p.
Acetylene Generators ... ... ... ... ... lU0to250c.p.
Oxygen with ordinary house gas used with blowthrough jet 300 to 500 c.p.
Oxygen gas compressed in cylinders and used tinmixing jet ... 1,000 to 1,500 c.p.
Oxygen with an independent Ether Saturator of good capacity, and used with a high-power
mixing jet 1,000 to 2,000 c.p.
The electric Arc light from ... 1,000 c.p upwards.
The best and most concentrated radient of light is derived from the electric arc, and most favourably from the arc of a direct current circuit, as it keeps the crater of the carbons in a more fixed position than if it were produced through an alternating current, which has a tendency to make the crater move round and so cause the luminous point of light to travel also, necessitating frequent adjustment,
At various places of public entertainment it is not uncommon for some operators to use a most powerful current through hand-feed arc lamps, taking as much as 50 to 100 amperes for throwing a light at a great distance, and from 20 to 40 feet in diameter upon the screen.
Electric Light and its Management for Projecting Purposes.
In houses where the electric light is laid on, it is a simple matter to obtain the electric current for the arc light. In most cases, it is best to call in the local electrician to examine the wiring and see whether the same is heavy enough to carry the amount of current required. If it is not, two wires should be joined somewhere near the main and brought in separate to the locality where the electric light would be used. This wire should be large enough to carry at least 25 amperes.
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