82 Mars during the Late Opposition. 



white disk on a black ground. On looking at the planet through 

 the telescope, it frequently happened that only the general 

 character of the markings upon it were discernible. The most 

 promiuent of these markings were at once noted on one of 

 the prepared circles, as quickly as possible, consistent with 

 accurate estimation and determination of their position. It 

 is important that this portion of the work should be promptly 

 executed, because the position of the markings rapidly changes 

 with the rotation of the planet. 



Having obtained the outline of the principal markings in the 

 manner above described, intervals of good definition were 

 watched for, aud upon their occurring, details of minuter 

 markings, colours, and shadows were successively filled in, 

 until in about an hour the drawing was completed. 



It will be understood that a drawing made in the manner 

 stated will show many features of interest that would escape 

 notice in a cursory observation. It will, in fact, represent the 

 most that can be made out by patient watching, with a tele- 

 scope of the aperture employed on the particular night. 



In the present drawings the planet is shown as it was seen 

 in the telescope. As inverting eye-pieces were alone used, the 

 lower white markings always represent the ice or snow on the 

 north pole of the planet, while the smaller light patches on 

 the upper part of some of the disks indicate the ice near the 

 south pole. I have made nearly thirty sketches at the telescope, 

 but I have carefully copied only thirteen. These were all made 

 when the air was tolerably stead} r , and the definition so good 

 that I could work well with powers above 200. Of this number 

 eight of the most interesting have been selected for repre- 

 sentation. 



When several sketches were made on the same evening, 

 they were taken at intervals of two hours, if the weather per- 

 mitted. In only one instance have I failed to make out that 

 the form of the markings was permanent, due allowance being 

 made for the effect of perspective in foreshortening them as 

 they approached the edge of the disk. 



It is highly probable that in the view of the planet taken on 

 February 16th, at 6'45, the two pointed markings on the extreme 

 left, one above, and the other below the equator, would have 

 been seen united if they could have been observed when they 

 were on the centre of the disk. This drawing would then 

 have agreed pretty closely with one of Mr. Dawes's views 

 engraved in the "Astronomical Register" for September, 186©. 



The colour of the body of Mars I have found vary from 

 roscTinadder to burnt ochre, the colour appearing ruddiest 

 when there was most mist in our atmosphere. The compara- 

 tive absence of the ruddy colour towards the edges of the 



