ENGINEERING: H. L. ABBOT 
41 
An examination of the rectangular coordinates resulting from the 
solutions (Table II) shows that nine out of the entire twelve values of 
Y and all of the values from the small Mck, are smaller for the northern 
than for the southern stars, indicating smaller average parallactic dis- 
placement for the northern than for the southern stars. 
Taking the stars of type B as the best marked example, if we use the 
value of Y derived from the southern stars to determine D for the northern 
stars, we obtain essentially the same D for both northern and southern 
stars, a value which agrees well with that obtained from the radial 
velocities of the same stars and with that from the radial velocities of 
all of the spectral classes. This will be true in principle also for the 
other cases, but appears to be complicated in the later types by other 
factors. 
Summary. — 1. The position of the apex of solar motion depends upon 
the proper motions in right ascension of the stars used. The differ- 
ences appear to be greatest in declination, the stars of large proper 
motion yielding apices south of those from stars with small proper motion. 
This effect is shown in the results both from proper motions and radial 
velocities. 
2. The differences in D of the apices of solar motion as derived by 
other investigators from radial velocities and from proper motions 
are consistent and they appear in general to be greater for the stars of 
late than for those of early type. This discordance appears to arise 
chiefly from the proper motions of the northern stars and to be satis- 
factorily explained by the assumption that the parallactic displacement 
■of the stars is systematically less in the northern sky. 
The details of this investigation have been sent to the Astro physical 
Journal. 
1 These Proceedings, 2, 1916, (376-378); Astroph. Chicago, III, 44, 1916, (103- 
116). 
' Contrib. Mount Wilson Solar Obs., No. 105. 
» Berkeley, Lick Obs., Univ. Cal., Bull., No. 196, p. 128. 
HYDROLOGY OF THE ISTHMUS OF PANAMA 
By Brig. Gen. Henry L. Abbot 
UNITED STATES ARMY. RETIRED 
Read before the Academy. November 13, 1916 
The Panama Canal being now opened to traffic, there remains for 
study only one important hydraulic problem — the sufficiency of the 
available water supply to meet the needs for lockage, for mechanical 
