196 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



0.00024690, from which the following probable errors have 

 been deduced : 



r x = ±0.0000130 and r = ±o°.03i= ±o°i'52". 



We, therefore, have from this solution 



Z=56°38'.8±i'.9 and x=-}-o.oooioi±o. 000013, 



giving 



loga=loga -{-o.oooioi [56°38'.8 — z]. 



We are, therefore, led to the conclusion that the so-called 

 Constant of Refraction needs not only a correction, but a 

 correction for every zenith distance. In other words, the 

 formula from which refractions are computed needs to be 

 modified. Or, the formula may be retained unaltered, and 

 the desired result obtained by correcting the log /* table of 

 the refraction tables used (Pulkowa) by the amount 



l\ log/*=o.oooioi [56°38'.8 — z]. 



R. T. C. 



