D. P. Todd—Solar Parallax from the Velocity of Light. 638 
89 _4 
ct sin z 
wherein g,,, denotes the mean anomaly of the earth, 
?,,. the angle whose sine is the eccentricity of the 
e ’s orbit, 
6, the constant of aberration. 
Struve’s constant of aberration, 20’4451, with Listing’s value 
of a, leads to the following results: The mean radius of the orbit 
of the earth equal to 
149,293,000 kilometers = 92,768,000 miles; 
and the mean equatorial horizontal parallax of the sun, 8’’°811. 
It remains to consider the probable variations of the elements 
of this computation, and the effect of such variations on the 
derived parallax. The following elements of sensible uncer- 
tainty are considered :— 
(1.) Uncertainty in the determination of the terrestrial 
velocity of light. In the process of experimental determina- 
tions of the velocity of light, almost no sources of mechanical 
most 
= V 0 cos 9, 
