PREFACE. 
In the spring of the year 1872, while the author was 
directing the photographic surveys of the United States 
Government on the Pacific Coast, there was revived in 
the city of San Francisco a controversy in regard to 
animal locomotion, which we may infer, on the authority 
of Plato, was warmly argued by the ancient Egyptians, 
and which probably had its origin in the studio of the 
primitive artist when he submitted to a group of critical 
friends his first etching of a mammoth crushing through 
the forest, or of a reindeer grazing on the plains. 
In this modern instance, the principal subject of dispute 
was the possibility of a horse, while trotting—even at the 
height of his speed—-having all four of his feet, at any 
portion of his stride, simultaneously free from contact with 
the ground. 
The attention of the author was directed to this 
controversy, and he immediately resolved to attempt its 
settlement. 
The problem before him was, to obtain a sufficiently 
well-developed and contrasted image on a wet collodion 
plate, after an exposure of so brief a duration that a horse’s 
foot, moving with a velocity of more than thirty yards in a 
second of time, should be photographed with its outlines 
practically sharp. 
In those days the rapid dry process—by the use of 
which such an operation is now easily accomplished—had 
not been discovered. Every photographer was, in a great 
measure, his own chemist; he prepared his own dipping 
baths, made his own collodion, coated and developed his 
own plates, and frequently manufactured the chemicals 
necessary for his work. All this involved a vast amount 
of tedious and careful manipulation from which the present 
generation is, happily, relieved. 
Having constructed some special exposing apparatus, 
and bestowed more than usual care in the preparation of 
the materials he was accustomed to use for ordinarily quick 
work, the author commenced his investigation on the race¬ 
track at Sacramento, California, in May, 1872, where he in 
a few days made several negatives of a celebrated horse, 
named Occident, while trotting, laterally, in front of his 
B 
