84 Mars during the Late Opposition. 



Mr. De la Eue lias shown the dark markings near the 

 south pole as darkest towards the edge nearest to the centre 

 of the planet, and just below the edge of the dark markings 

 the ruddy colour of the body as much fainter than it is nearer 

 to the centre of the body about the equator. I see these 

 appearances distinctly. 



In the drawing taken on January 28th, at 9h, a number 

 of breaks will be seen in the edge of the dark marking near 

 the south pole,, and forming a series of light streaks directed 

 towards the pole. Mr. Barnes also sketched this appearance, 

 without seeing my sketch, and as, with the exception of a 

 slight difference in the angle given to the light streaks, the 

 two sketches agreed, I cannot have been mistaken in their 

 appearance having been as I have drawn and described them. 



On the 31st of March, at 7h, I obtained an exact repetition 

 of the markings in precisely the same position shown in the 

 drawing taken on February 23rd at 9h. ; the two drawings 

 coincide so perfectly that I can only distinguish between them 

 by the dates affixed to them. In these two drawings the 

 mark usually termed the hour-glass mark is represented as 

 having just passed the centre of the disk of the planet. The 

 movement, in the time I have stated, includes a period of 

 35 revolutions, and the time of a single revolution on its axis 

 deduced from the observed recurrence, would be 24h. 38m. 8s. 

 Beer and Madler, who have observed the largest number of 

 revolutions, give the period of rotation as 24h. 37m. 23s. My 

 own determination is, however, less than Sir ¥m, Her seller's. 



Could a repetition of the markings in exactly the same 

 position have been observed after a much greater number of 

 revolutions had been completed, a period of revolution more 

 closely accordant with B. and M.'s determination would pro- 

 bably have been obtained. The very unfavourable weather we 

 have had to contend with for some months, has, I regret, 

 rendered a repetition of the observations impossible. 



I have said elsewhere that between my own drawings, Mr. 

 De la Rue's, and Mr. Dawes's, there exists a great similarity, 

 and to one of Secchi's drawings one of mine has a considerable 

 resemblance, but I cannot trace a likeness between any of my 

 views and those of Beer and Madler. This observation leaves 

 on the mind a suspicion that in the course of time some change 

 may have taken place. With regard to the point that no flatten- 

 ing of the planet at the poles has been detected, even by that 

 admirable observer, Mr. Dawes, I would remark that although 

 if the sphere of the planet were oblate to the extent of one- 

 sixteenth, or one-tenth of its diameter, as in the case of Jupiter 

 and the globe of Saturn, the flattening might be easily dis- 

 cerned, yet, if the flattening should not exceed, in proportion, 



