108 Mr. Baity on the ensuing Opposition of Mars. [Feb. 



the last opposition in 1822, I ventured to draw the public atten- 

 tion to the subject, by pointing out certain stars, near which the 

 planet would pass ; and with the positions of which it might be 

 compared. Several valuable observations were made both in the 

 southern and in the northern hemisphere, which are published 

 in various periodical works ; and which being thus recorded, 

 may be referred to with advantage, by those who devote them- 

 selves to this branch of physical astronomy. 



At the present opposition, there are but few stars, and those of 

 inferior magnitude, with which Mars can be advantageously 

 compared. For ten days preceding and subsequent to the date 

 of its opposition, Mars will not approach near to any star given 

 in the large catalogues of Bradley or Piazzi. There are, however, 

 five stars given in the catalogues of Lalande, inserted in the 

 Connaissance des Terns for the years VIII. and XIII. with which 

 the comparisons may be made. The mean places of these stars, 

 on Jan. 1 of the present year, are given in the following little 

 table ; together with the dates when Mars will be in conjunction 

 with them. 



When Mars approaches either of these stars, the observer 

 should, with a micrometer, measure their distance, in a direct 

 line, or take the differences, in right ascension and declination, 

 between the planet and the star ; the place and the correct time 

 of observation being noted down. 



Accurate observations of this kind are of great importance in 

 astronomy ; and as nothing tends so much to further such objects 

 as a previous announcement of the phenomena about to take 

 place, I trust I need not make any apology for drawing the atten- 

 tion of the members of this Society to so interesting a subject. 



The diameter of Mars, on the day of opposition, will 

 be 13-91". 



