INTRODUCTION. 
as a factor in scientific research was beginning to be recog¬ 
nized. Since then it has been the means of opening many 
new fields for inquiry, and a number of important dis¬ 
coveries have been made which without its aid would 
have been impossible. 
It was to photography, therefore, that the author 
resorted when he commenced a solution of the complex 
problem of “ Animal Locomotion.” The origin of his 
i r 
labours has been mentioned in the Preface. Before 
attempting a description of the results, it is essential 
that the system employed for their obtainment should 
be understood. The investigation at Palo Alto was 
conducted in practically the same manner as that at the 
University of Pennsylvania; it will, therefore, be sufficient 
to give a general explanation of the studio arrangements 
at the latter place. 
Diagram of the Studio at the University of Pennsylvania, and Arrangement of the 
_ Apparatus for investigating Animal Locomotion. 
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