APPENDIX. 125 



This arrangement gave the attitude of the horse as he arrived 

 before each of the cameras in succession at the instant of exposure of 

 the negatives. In practice it was found to be extremely difficult to 

 set the apparatus in motion at the exact time required, and to regulate 

 it to correspond to the speed of the horse. 



This contrivance was found to be best adapted to the more irreg- 

 ular movements of other animals, as the running of dogs, the flight of 

 birds, feats of acrobats, etc. It was desirable to find some method 

 that would better represent the regular movements of the horse, and 

 which should be regulated by his own movements. 



On the side of the track opposite the building where the cameras 

 were placed, and in such position as to receive the best exposure to 

 light, a wooden frame was erected, about fifty feet long and fifteen 

 high, at a suitable angle, and covered with white cotton sheeting 

 (Plate CVII.), divided by vertical lines into spaces of twenty-one inches, 

 each space being consecutively numbered. Eighteen inches in front 

 of this background was placed a base-board twelve inches high, and 

 on which were drawn longitudinal lines four inches apart. In front 

 of this base-board a strip of wood was fastened to the ground, upon 

 the top of which wires were secured at an elevation of about an inch 

 above the ground and extending across the track. The wire was 

 exposed in a groove to one only of the wheels of the sulky, being 

 protected from contact with the horse's feet and the other wheel. 

 Each wire was held in proper tension by a spring on the back of the 

 base-board, so arranged that when the wire crossing the track was 

 depressed by the wheel it should draw upon the spring connected 

 with it, and make contact with a metallic button and complete the 

 electric circuit. 



These wires were placed at distances from each other correspond- 

 ing with the cameras on the opposite side of the track, and with the 

 spaces between the lines drawn on the background. 



From this description it will be readily seen that the depression of 

 the first wire would complete the circuit and cause the magnet con- 

 nected with the corresponding camera to move the latch and liberate 

 the shutters, exposing the sensitive plate for a space of time that is 



