1 mile per hour moves 1-1/2 feet per second.
2 " " 3 " "
5 " " 7-1/2 " "
6 " " 9 " "
7 " " 10-1/2 " "
8 " " 12 " "
9 " " 13 " "
10 " " 14-1/2 " "
11 " " 15 " "
12 " " 17-1/2 " "
15 " " 22 " "
20 " " 29 " "
25 " " 37 " "
30 " " 44 " "
35 " " 51 " "
40 " " 59 " "
45 " " 66 " "
50 " " 73 " "
55 " " 80 " "
60 " " 88 " "
75 " " 110 " "
100 " " 147 " "
125 " " 183 " "
150 " " 220 " "
200 " " 257 " "
With these tables it will be very easy to find the distance that the
image of the object will move on the ground-glass screen of the camera.
To do this, multiply the focus of the lens in inches by the distance
moved by the object in the second, and divide the result by the
distance of the object in inches.
[Illustration: FIG. 81.--"A RISE IN THE WORLD." BY THE MARQUIS DE
ALFARRAS.]
Example, find the movement of the image of an object moving 50 miles
per hour at a distance of 100 yards with a lens of 9-inch focus.