542 
Smith—Stadia Measurements. 
The latter will be called primary , and the former secondary vi¬ 
brations. The effect of this unsteadiness on the appearance of 
theTarget is shown in Fig. 3. 
80° 82° 89° 95° 98.5° 96 8° F„ 
i 
1 
1 
m 
Fig. 8—Typical Disturbance Curves Showing the Effect of Time of Day, Tempera¬ 
ture, and Length of Sight on Degree of Unsteadiness. 
X-time of day. 
Y— amplitude of vibration. 
Fig. 9.—Disturbance Curves Showing the Effects of Clouds on Unsteadiness. 
X—distance of sight. 
Y= amplitude of vibration. 
The manner in which these two systems occurred, can be 
best shown by a diagram. (Fig. 4.) If the crosswire could re¬ 
cord its apparent motion it would describe a path like that in 
Fig. 4, where B—D limits the amplitude of the primary vibra¬ 
tion, and the irregularities of the path constitute the secondary 
system. The manner in which the amount of this vibration 
is influenced by length of sight, hour of day, brightness of 
sun, temperature, etc., can be best shown by the typical curves 
representing the same. 
