170 
ASTRONOMY: A. 0. LEUSCHNER 
Proc. N. a. S- 
turity, should assist materially in revealing the cause of spot formation. 
Their frequency of occurrence is probably much greater than these first 
results suggest, as our winter observations have been seriously limited 
by exceptionally cloudy weather, poor seeing, and low solar activity. 
^ Hale, On the Probable existence of Magnetic Fields in Sun-spots. Mount Wilson 
Contr., No. 30; Astroph. J., Chicago, 28, 1908 (315-343). 
2 Hale, Ellerman, Nicholson, and Joy. The Magnetic Polarity of Sun-spots. 
Mount Wilson Contr., No. 165; Astroph. J., Chicago, 49, 1919 (153-178). 
COMPARISON OF THEORY WITH OBSERVATION FOR THE 
MINOR PLANETS lo HYGIEA AND 175 ANDROMACHE WITH 
RESPECT TO PERTURBATIONS BY JUPITER 
By. a. O. Leuschnkr 
Department of Astronomy, University of Cai^ifgrnia 
Read before the Academy, April 24, 1922 
The perturbations of the minor planets 10 Hygiea and 175 Andromache,, 
developed by Dr. Kstelle A. Glancy and Dr. Sophia H. Levy on the basis 
of the revision of von Zeipel's formulae and tables of minor planets which 
have a mean motion approximately twice that of Jupiter, (Hecuba Group),, 
have lately been severely tested by comparison of recent observations with 
the computed places, for which the numerical work was performed by 
Dr. H. Thiele. This revision of von Zeipel's theory will soon appear as 
the third memoir of Volume 14 of the Memoirs of the Academy. The 
results of these comparisons are highly encouraging and prove that the 
revised tables for the Hecuba Group more than meet the practical require- 
ments of a satisfactory representation of the motion of the minor planets 
belonging to this group. The preliminary conclusions communicated ta 
the Academy at the annual meeting of 1916 in my general report on the 
perturbations and tables of the minor planets discovered by James C. 
Watson are thereby fully verified. 
Hygiea was discovered on April 12, 1849 by Gasparis. The most 
accurate of the earlier orbits computed was that by von Zech, which was 
based on the elements of d'Arrest and the general perturbations, developed 
by Hansen's method, by Jupiter, Saturn, and Mars, extending over eight 
oppositions. Since von Zech's death in 1864, his computations have been 
kept in the Recheninstitut at Berlin and were used by von Zeipel in con- 
nection with the application of his approximate perturbations for the 
Hecuba Group. Von Zech's computations have been continued from year 
to year at the Berlin Recheninstitut until 1873, up to which time they 
represented the motion of Hygiea with considerable accuracy. In the 
Berlin Jahrbuch for 1876 new elements by E. Becker are given. These 
