XX.—NOTES ON THE PHYSICAL APPEARANCE OF THE PLANET 
MARS DURING THE OPPOSITION IN 1881. ACCOMPANIED BY 
SKETCHES MADE AT THE OBSERVATORY, BIRR CASTLE. By Orro 
Bapoicxsr, Pa.D.—Wirn Pirates XXXVI. ann XXXVII. 
Communicated by the Earl of Rosse. 
[Read April 17th, 1882.] 
Tux drawings of the planet Mars, which accompany these notes, were made with 
the reflector of three feet aperture at the Earl of Rosse’s Observatory, Birr Castle, 
Parsonstown, from 1881, Nov. 19, to 1882, January 23, both days included. 
Unfortunately, the weather was very bad during this period, so that it was im- 
possible to obtain more than twenty-one drawings, eighteen of which are here 
selected for publication. It would doubtless have been practicable to observe the 
planet with advantage after the 23rd January, if it had not also been frustrated by 
the unfavourable state of the atmosphere. 
The speculum used is the same with which the drawings of Comets b and ¢, 
1881, in these Transactions, Part XVIL., (antea page 239 and Plate XIX.) have 
been executed ; the power was in all cases 216. 
The drawings are reproduced as they were made before the telescope. The most 
conspicuous spots were first put down and the time noted, and the more difficult 
details gradually filled in in the same degree as they could be discerned with 
certainty. The time spent upon each sketch was half-an-hour on the average, 
For sketching the stump alone was used, as with it the peculiar character 
of the markings could be best imitated. The amount of the phase has not 
been applied to the drawings, as they will hardly be of much value for the 
determination of areographic longitudes, being based on rather hurried eye-estima- 
tion only. | 
The following notes, in which the time referred to is mean Greenwich time, were 
made during the observations. The longitudes, after which the drawings are 
arranged, have been taken from Marth’s Ephemeris in “ Astronomische Nachrichten, 
No. 2,395.” 
1881, November 19. 
Drawing No. 13.—Longitude, 2878. Time, 12% 32™. 
Pretty clear, but the smoke of the observatory chimney sometimes in the way. 
The dark markings, especially the one on the central meridian, dark bluish ; the 
large following continent (slightly shaded in drawing) very strikingly orange ; limb 
very bright, especially north pole. 
TRANS. ROY. DUB. SOC., N.S, VOL I. 3C 
