An Experimental Study of Field Methods. 
541 
Figs. 5, 6, and 7 .—Typical Disturbance Curves Showing Effect 
of Hour of Day and Length of Sight on the Degree of Un¬ 
steadiness. 
X—distance of sight. 
Y— amplitude of vibr. 
Fig. 4.—Typical Vertical Vibrations. 
