ANIMATED PICTURES. 181 



a standstill. At the same time a shutter * is opened and an image 

 of the picture flashes for an instant upon the screen. The shutter 

 is then quickly closed, the picture resuming its motion, while its 

 successor in the series is brought into a similar fixed situation. 



This temporary stoppage of the film (or rather of a portion 

 thereof), as each picture attains its proper place behind the pro- 

 jecting lens, is a very essential feature of the process. It is effected 

 by various ingenious devices, among which those of Acres, Edison, 

 and the Lumiere brothers are deserving of special notice. Without, 

 however, attempting to describe these diverse forms of apparatus, I 

 will try to indicate in general terms the means by which an inter- 

 mittent motion of the film is secured. Let us assume that a picture 

 has arrived at the fixed position already referred to. At the instant 

 of its arrival, a portion of the film on the preceding side of the pic- 

 ture will be in an unstrained or slack condition. The " slack " is 

 then taken up by a continuously moving sprocket pulley, whereupon 

 a rod or roller is quickly brought to bear against the now tightened 

 film, pressing it to one side and as quickly releasing it. By this 

 movement the next picture is pulled into its fixed position, while 

 the film is made taut (or nearly so) on the following side of this pic- 

 ture. These operations are repeated continuously until the entire 

 film has passed through the holding device in rear of the lens. The 

 process may be compared, in a general way, with the automatic feed- 

 ing of a web of paper to an ordinary printing press. 



A specially constructed camera is used in taking the negatives 

 from which ultimately motion pictures are obtained. This camera 

 is provided with mechanism generally similar to that employed in 

 showing the photographs, f Indeed, the selfsame mechanism has 

 frequently been used for both purposes. The picture roll is replaced 

 by a reel of sensitized film, upon which the exposures are made in 

 quick succession when the apparatus is set in motion. From twenty- 

 five to fifty photographs are thus " laid on " in a second of time. 

 The films range in length from fifty to two hundred feet, and contain 

 when finished from eight hundred to more than three thousand tiny 

 negatives. 



After exposure the film is subjected to the usual photographic 

 operations. These are, however, conducted with special arrange- 

 ments, rendered necessary by the inordinate length of the film. 

 The latter is subsequently made to pass, in contact with a second 



* In some forms of apparatus, such as the vitascope and phantascope, the shutter is 

 omitted. The intermittent motion of the film does not seem to mar the continuity of the 

 pictures, which are also more fully illuminated in the absence of a shutter. 



t The Jenkins camera (see illustration) forms an interesting exception to this general 

 rule. 



