546 
Smith—Stadia Measurements. 
the ground; the results of which are given a graphical form in 
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are the heights of the targets above the ground; and they ordi¬ 
nates are the products of the number of vibrations per minute 
and their amplitude. It will be seen that, between one-half and 
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Fig. 14. —Typical Disturbance Curves Showing the Effect of Height of Line of 
Sight on the Degree of Unsteadiness at 12 O’Clock July 25,1898. 
X=height of target (in meters). 
Y=Product of number of vibrations by their amplitude. 
one meter, a rapid change in the amounts of unsteadiness was 
found; while between one and four meters, the change was very 
slight. Thus in Fig. 13, the 200 meter curve shows that the 
rate of change in the unsteadiness between one-half and one 
meter was 18 times that between one and four meters. 
The remarkable refraction which takes place in this stratum 
of greatest unsteadiness may be explained by the peculiar shape 
