118 MOVEMENT 



thick. The bobbins rotate on a vertical pin which 

 runs through their centre. A circle of little holes 

 bored in the lower plate of the bobbin forms part 

 of the motor mechanism. When a peg fixed in a 

 revolving plate enters one of the holes of the other 

 plate, the two will rotate together, carrying the bobbin 

 with them. 



One of these bobbins serves to store the sensitized 

 film, which is rolled round it, and which is finished off 

 at the ends by strips of opaque paper pointed at the 

 extremities. One of these pointed ends fits into a slit 

 made lengthways in the bobbin, and the rolling up can 



fT ~ T ~ : " 



Sensitized film 



Fig. 83.— Showing liow the film is lengthened at its two extremities by the opaque 

 bands of paper. 



thus be effected. In the process of rolling, the strip 

 of paper comes first, then the sensitized film which is 

 joined to it, and then the second strip of paper. An 

 elastic band put round the bobbin keeps the entire roll 

 securely fastened. This operation is executed in the 

 dark room, but as soon as it is finished the charged 

 bobbin can be carried into the light, for the sensitized 

 film is protected by the coils of opaque paper. 



Charging the Apparatus. — On opening the photo- 

 graphic ch amber, two vertical pins may be seen 

 (Fig. 80) ; that on the left receives the supply bobbin, 

 the filling of which has already been described, and 

 that on the right is for the receiving bobbin — that is to 

 say, the one which will receive and roll up the film, or 



