HINTS ON EXHIBITING.
Absolute rigidity of the stand and apparatus must be secured. A hollow body should not be used for this purpose, since it will not only tend to cause vibration but will distressingly increase the noise. The machine should be well oiled before use with good clock or cycle oil, and a small quantity of vaseline should be placed on the spool spindles. The light must be well centred on the screen before the film is inserted. While inserting the film, and when ever the latter is not in motion, the drop shutter or other device must be used to cut ofl the light, or the heat from the condenser may cause the stationary film to catch fire. The amount of picture shown is adjusted by a masking device, which will vary with the construction of the apparatus. During the intervals of inserting fresh films, etc., the audience should be kept interested by the display of ordinary lantern slides. " Reversing "—i.e. passing a film through the machine end first—is sometimes employed to produce unusual and humorous effects ; as the pictures will, of course, be upside-down, a reversing prism or mirror is required on the Glycerine has also been used for the same purpose. Messrs. Lumiere are responsible for
the introduction of a spherical glass flask filled with water, which serves both as a con denser and a heat-absorber. At the upper portion of the flask a small piece of carbon is suspended to withdraw the gases liberated by the gradual heating of the water.
projecting lens to erect them. Comic films of this description are now, however, more usually reversed when made, so that reversal in the lantern is unnecessary. After a film has been shown it requires re-winding ; for this purpose several convenient forms of winder are made ; while, in some projectors, the top spool is supplied with a re-winding gear, which can be brought into action when required.