eee et Re 
298 W.A. Rogers on Variability of Personal Equation. 
The results on which this discussion is founded depend upon 
about 8,000 observations of artificial stars, In the present 
instance, the artificial stars were made of paper and centered 
upon fine steel wires placed in a vertical position. Now itis 
evident that if the wire to which the star is attached, could be 
made to pass a stationary vertical wire with a uniform motion, 
and if the exact time of opposition could be automatically re- 
corded, we should have a standard with which the observed 
time of passage could be compared. The following device was 
employed to accomplish this object. 
47’ is @ wire insulated with respec 
work at i and 7’ but in contact with it at z. To the endof 
this wire is attached a fine needle 2” 4” projecting beyond the 
plane of the wires on the cylinder just far enough to come ™ 
contact with them as they revolve. The wires ww’ run to ® 
battery after passing through a coil (not represented in the 
figure) with which the pen p p’ is connected. es 
. As the cylinder revolves, the instant b 0’ arrives opp aa : 
of con” 
one bb. 
