ASTRONOMY: A. 0. LEUSCHNER 
73 
case, (133) Cyrene, which although approaching the Hecuba type had been 
developed by Hansen's method in the early stages of our investigations. As 
the observation used in this case, however, is only approximate, a further test 
may show the slight discrepancy to be erroneous. These comparisons repre- 
sent a remarkable result for the published tables, as in these cases some twelve 
years had elapsed since the last opposition used for the correction of the 
elements and for the tables. 
In conclusion I may refer briefly to two of the most interesting Watson 
planets. 
The Watson planet which promises to become one of the most interesting 
of the twenty-two under consideration, if not of all the 1400 or more so far 
discovered, is (175) Andromache, which belongs to the Hecuba group, or 
group 1/2, the mean daily motion being approximately twice that of Jupiter. 
Andromache was found by Watson on October 1, 1877 and was the last but 
one discovered by him, his latest discovery, as stated before, being (179) 
Klytaemnestra on November 11, 1877. Andromache was assiduously ob- 
served for one month, 43 observations at widely scattered observatories being 
secured by the most competent observers. The calculation of the orbit 
yielded a mean motion of approximately 550". In spite of diligent search 
the planet was not found again from any predictions based on the original 
elements. This failure to find Andromache is a striking illustration of the 
fallacy of some of the orbits included as thoroughly reliable in our published 
lists. On May 19, 1893 a presumably new planet was discovered at Nice 
and given the provisional designation 1893 Z. From observations extending 
over more than two months an orbit resulted resembling the orbit of Androm- 
ache, except for the mean motion which was found to be at first 617" and 
later 610." 
The following possibilities existed then with reference to Andromache and 
1893 Z. (1) the planets might be identical, the adopted mean motion of 
550'' of Andromache being erroneous. (2) The planets might be identical 
•and the mean motion might have changed from the smaller value of 550" to 
the larger value of 610," passing through 598" which is twice the mean motion 
of Jupiter. If this were true a phenomenon of the utmost importance to 
■science, known as libration, would come under consideration. (3) The 
planets might not be identical. 
A study of the observations of Andromache revealed an uncertainty of the 
comparison star of one of the fundamental positions. From the orbit of 
1893 Z positions were then calculated for the dates of observation of Androm- 
ache in 1877 and a satisfactory agreement found. The identity of the two 
planets was thus estabhshed in 1893-94. At the same time the hope for the 
occurrence of the first case of libration for a planet of the group 1 /2 was shat- 
tered, for the mean motion in 1877 turned out larger by several seconds than 
the 610" calculated for 1893. On the basis of these computations Androm- 
ache was also found on some Heidelberg plates taken in 1892. 
