354 



TRANS. ST. LOUIS ACAD. SCIENCE. 



sion of the relative merits of reflectors and refractors, excited by 

 the observations of these satellites, it may be interesting to many 

 to try if they can see them. 



In the case of Deimos, the outer satellite, the ephemeris gives 

 the Washington mean times of the east and w^est elongations' 

 together with the position -angle and distance at the time of 

 elongation. In the case of Phobos only the times of western 

 elongations are given as the revolution time is very short and the 

 times of eastern elongations may be obtained by a simple inter- 

 polation. The aberration time is not included in the time given, 

 but it may be taken from the table at the end if desired, the effect 

 of the aberration being to make the satellites about five minutes 

 late at each elongation. The relative brightness on different days 

 may be obtained from the same table, taking the brightness on 

 Nov. 20 as unity. As was shown by the observations of 1879, 

 Prof. Hall's elements are very nearly correct, so that the correc- 

 tion to this ephemeris will be quite small. 



DEIMOS. 



