172 
ASTRONOMY: A. 0. LEUSCHNER 
Proc. N. a. S. 
and that several experiments by Miss Glancy, the last published in 1918 
in the Astronomical Journal Number 748, to remove outstanding differ- 
ences between theory and observation by correcting von Zech's elements 
have led to invalid results, as in the case of von Zeipel's earlier attempt 
in the same direction. 
Outstanding differences between theory and observation are of the sai;ne 
order of magnitude in the two intervals. In fact in 1917 the discrepancy 
was less than 1' in both right ascension and declination, although in a 
very few of the long series of oppositions positive or negative differences 
as high as 10' exist in right ascension. These differences however, are 
primarily due to perturbations by Saturn which so far have not been 
taken into consideration. These encouraging results on Hygiea clearly 
show that on the basis of the revised tables for the Hecuba Group and 
on the basis of reliable elements determined from a very few oppositions, 
perturbations may be developed for all planets of this group which will 
yield a satisfactory theoretical representation of observations for practical 
purposes. It is safe to say that the abandonment of the piece-meal method 
of computing special perturbations and correcting elements from opposi- 
tion to opposition in favor of the group theory will release in the long run 
a considerable part of the efforts of the astronomers who are engaged in 
these laborious tasks. 
175 Andromache was discovered by Watson on October 1, 1877. A 
preliminary report on the perturbations of this planet was rendered at 
the annual meeting of the Academy in 1916. At that time it was pointed 
out that as shown by the very accurate computations by Berberich at the 
Recheninstitut of the special perturbations of Jupiter and Saturn, the mean 
motion had constantly decreased from 617.7 in 1877 to 607.9 in 1910. 
During the last ten years the osculating mean motion has decreased but 
slightly. According to Miss Levy's development of the perturbations of 
Andromache by the revised tables this decrease in the osculating mean 
motion is due in the main to three long period terms of Jupiter's pertur- 
bations having a period of approximately 187, 94, and 62 years, with an 
amplitude of 23.3° for the perturbation of longest period. By introducing 
the effect of these long period terms into the mean motion. Dr. Thiele, 
who has made the necessary computations, and I have approximately 
reproduced the nearly progressive change in the osculating mean motion 
as computed by Berberich. By extending this process, we may predict 
that the minimum value of the osculating mean motion is nearly reached and 
that within the next few years it will begin to increase. A case of libration is 
therefore not involved as the mean motion will not pass through the value 
which is twice that of Jupiter. The maximum value will be reached be- 
tween the years 2004 and 2016, after which it will again decrease. In 
fact, none of the cases of planets of the Hecuba Group so far examined 
