INSTANTANEOUS PHOTOGRAPHY. 11 



openings were made in the disks where the hands should be, and 

 a camera lens placed behind the noon-mark of the clock, an image 

 would be got at twelve o'clock. The fast disk would return its 

 opening in an hour, but the two openings would not coincide till 

 5fj minutes past one, which w^ould be past the lens. 



The two disk openings would again come together at 10^ min- 

 utes past two, but the three openings and those in the disks and of 

 the lens would not coincide till twelve o'clock, when another image 

 could be impressed. 



The disks were circular saw-blades with four balanced openings, 

 over which openings gossamer waterproof was stuck by Venice 

 turpentine, thickened by heat and spread on the edges. In this 

 waterproof openings were cut radially as wanted. 



A crank turned by hand communicated to the disks through a 

 belt going from a large to a small pulley the requisite speed. 



Between the disks and the lens was fitted an electric shutter. 

 The disks revolving, and the object set in motion, the observer, 

 with his fingers on the key-board, presses the first button when 

 he wishes the impressions to begin, and the second button when 

 lie wishes them to end. 



Pressing the first button breaks contact in an electric circuit 

 that holds against the force of a rubber spring, the armature of an 

 electro-magnet controlling the trigger, which releases in the shutter 

 an opaque slide covering the lens opening. The second button of 

 the key-board releases in the same way a similar opaque slide, 

 which, having been held in place above the lens, now comes down 

 in front of it. 



The shutter was constructed to move very rapidly. The slides 

 are little squares of silk waterproof, kept stretched by pieces of 

 quill, silk wrapped, attached to the corners. These quills slide 

 vertically, on brass rods, and the slides are pulled down by india- 

 rubber bands, which reach down all the way to the floor. The 

 bands used are the little parcels bands, looped end to end until 

 sufficient length is got. 



The reason for using long bands is this : friction overcome, 

 rapidity is got from length, not thickness of spring. For in- 

 stance, two gum bands, side by side, stretched and released, 

 would not travel faster than one of them ; but if looped end 

 to end the speed of the one adds itself to the speed of the other. 



