18 



THE MECHANISM OF 



inside of it was painted white, like the camera-house, that they 

 mig-ht reflect lio-ht towards the centre of tlie track. The entire 

 length of the camera-house front, thirty-two feet, could be thrown 

 open by a number of shutters about two feet wide swinging upward. 

 Inside the camera-house, and running almost the whole length of it, 

 was an immovable table or counter, on M'hose level top were placed, 

 side by side, a battery of twenty-four four by five inch cameras, 

 twelve of which are represented at L, with their lenses at a per- 

 pendicular distance of about fifteen metres (forty-nine feet) from 

 the line of progressive motion on the track indicated by the arrow 

 I, and fifteen centimetres, or six inches, apart between successive 

 centres. These lenses are perfectly rectilinear, three inches in 

 diameter and fifteen inches equivalent focus, and were ordered 

 from England by one of the guarantors of the expenditures as- 

 sumed by the University of Pennsylvania expressly for these 

 investigations. In front of each camera was an electro-photo- 

 graphic exposor, an improvement on those which Mr. Muybridge 

 had previously invented and used in California. A view of the 

 camera-house, with the row of large exposors inside of it, is shown 



in Fig. 4. 



Fig. 4. 



Fig. 5 is a diagrammatic side view of an exposor and its re- 

 leasing magnet. The exposor proper, A, is a continuous curtain 

 of black rubber-cloth, thin but perfectly opaque, moving easily on 

 the two rollers R and R. In this curtain are two openings, O and 

 O, so placed that they come directly opposite each other in front 

 of the lens L. Motion is imparted to the curtain by the tension 



