APPARATUS ' 25 



of ground in a second of time; a full mile averaging 

 perhaps a hundred seconds. At this speed, a foot re- 

 covering its loss of motion will be thrust forward with 

 an occasional velocity of at least 120 lineal feet in a 

 second of time. 



During the one one-thousandth part of a second the 

 body of the horse will at this rate move forward about 

 seven one-tenths of an inch, and a moving foot perhaps 

 one and a half inches, not a very serious matter for the 

 usual requirements of the amateur photographer. 



A knowledge of the duration of the exposures, 

 however, was in this investigation of no value, and 

 scarcely a matter of curiosity, the aim always being to 

 give as long an exposure as the rapidity of the action 

 would permit, with a due regard to the necessary 

 sharpness of outline, and essential distinctness of detail. 



The power used for operating the magnets, through 

 the exposing motor, was given from a le Clanche 

 battery of fifty -four cells, arranged in multiple arc of 

 three series, each of eighteen cells. 



During the investigation at the University of Penn- 

 sylvania, more than a hundred thousand photographic 

 exposures were made. 



The negative plates were supplied by the Cramer 

 Dry Plate Company of St. Louis, and the positive 

 plates by the Carbutt Company of Philadelphia. On 

 a favorable day five hundred or six hundred negatives 

 were sometimes exposed; on one day the number of 

 exposures reached seven hundred and fifty. 



The electrical manipulations were directed by Lino 

 F. Rondmella; the development room was in charge of 

 Henry Bell. The author takes pleasure in acknowl- 



