48 J. H. Lane on an Automatic Comparison of Time. 
5 . . . os * 
A. similar optical means can also be used for comparing 4 
mean time cloc I 
: po - irror, 
either a flash or an interruption of light from the other 
station may be observed by reflection, and the coincidence no 
when the flash or the break is seen at the same point of the field 
of view where it is observed with the pendulum at rest. 
sons by means of a sufficient number of th instruments 
re ww | e visual ins 
