ANIMALS 
synchronous action of ten of the duplicated series ; and in 
the two others there was a discrepancy in the simultaneity 
by a few ten-thousandths of a second; a result sufficiently 
near to synchrony for any ordinary use. 
The shortest exposures made at the university were 
in about the one six-thousandth part of a second, and 
in this time details in black and white drapery were 
obtained on the same negative. Such brief exposures 
were in this class of work rarely needed. Some horses, 
galloping at full speed, will cover nineteen yards of ground 
in a second of time, or a full mile in a hundred seconds 
or less. At this speed a foot, recovering from its rest, 
will be thrust forward with an occasional velocity of more 
than forty yards in a second. During the one-thousandth 
part of a second, the body of the horse may move forward 
about seven-tenths of an inch, and a moving foot perhaps 
one and a half inches—-no very serious matter for ordinary 
requirements. 
A knowledge of the duration of the exposure was in 
this investigation of no value, the aim always being to 
give as long a time as the rapidity of the action would 
permit, with a due regard to essential sharpness of outline 
and distinctness of detail. 
Although the one six-thousandth part of a second was 
the most rapid exposure made on this occasion, it is by 
no means the limit of rapidity in mechanically effected 
photographic negative exposing; nor does the one-hun¬ 
dredth part of a second approach the limit of time-intervals. 
Marey, in his physiological experiments, has recently made 
MOTION. 
successive exposures with far less intervals of time ; and 
the author has devised, and hopes some day to make use 
of, an apparatus which will photograph twenty consecutive 
phases of the vibration of an insect's wing, even assuming 
as correct a quotation by Pettigrew from Nicholson s 
Journal , that a common house-fly will make, during flight, 
seven hundred vibrations in a second—a number probably 
much in excess of the reality. 
It may be here appropriately mentioned that Marey, 
in 1882, discarded his original “graphic” method of 
analyzing motion for the more effective photographic 
process. 
At the Palo Alto investigation a series of negatives 
was frequently made by threads stretched across the track 
of the animal. The thrust against each of these threads 
in succession completed an electric circuit, and effected a 
photographic exposure; the thread was subsequently 
broken by the progress of the animal. Some seriates were 
made by the wheel of a vehicle, to which a horse was 
attached, depressing wires ; each depression completed a 
circuit and effected the exposure of a negative. For small 
animals and birds, and for movements without regular 
progressive motion, the motor-clock was necessarily used. 
The rapidity of the transmission of nervous sensation 
was experimented with. The explosion of a small torpedo 
in close proximity to an animal or bird, started the motor- 
clock, and commenced a series of exposures. An example 
of its effect may be seen in Plate 781 of “Animal Loco¬ 
motion.” 
