468 J. M. Schaeberle—Lateral Astronomical Refraction. 
actually lies, while the first expression gives the displacement 
in zenith distance, 
As the corrections resulting from the introduction of the 
term = would only be applied to observations made with the 
best instruments, we need but deduce the formule, and tables 
for the corrections to meridian observations. In other words 
the corrections to the observed times of meridian transit, and 
to the reduced zenith distances. Let da and dz denote these 
corrections, then we evidently have, since 2’’=0 
@ oh 
were TI D cos z sin Y sec 0 
dea sec? z cos W, 
practically the same amount, and as we have only to deal with 
the differences in the refractions at the two stations, the results 
obtained will not, in general, be sensibly in error. The last 
equation, if we neglect small quantities, can be put into the 
following form : 
rr =a(e (T,—T,) +Pe—Ps) tan zZ. 
0 
his value of a is 57’ 
See Chauvenet’s Spherical and Practical Astronomy, vol. i, p. 160. 
