1863.] 431 



II. " On the Telescopic Appearance of the Planet Mars." By 

 JOHN PHILLIPS, M.A., LL.D., F.R.S, F.G.S., Professor of 

 Geology in the University of Oxford. Received February 

 5, 1863. 



Notwithstanding the descriptions and drawings of Mars, for which 

 we are indebted to eminent observers*, there remains much uncer- 

 tainty as to the permanent boundaries of the bright and shady parts 

 of the planet, to which respectively, on a first view, we attach, per- 

 haps too readily, the idea of land and seas. The extremely variable 

 aspects under which this planet appears in its excentric orbit, the axis 

 being inclined more than 30 to the ecliptic, the different regions very 

 unequally presented to incident light, and very unequally influenced 

 by vicissitudes of heat and cold, may account for much of the uncer- 

 tainty. Other difficulties arise when the work of different instru- 

 ments is compared ; for it is established that reflectors will on the 

 whole give the best results for colour, while achromatics of fine 

 quality discover more of detail than instruments of less perfect 

 definition. 



The author having devoted some evenings between the 27th of Sep- 

 tember and 13th of December 1862 to the examination of Mars with 

 a 6-inch achromatic by Cooke, equatorially mounted, and moved by 

 clockwork, at Oxford, presented to the Society some results of these 

 observations combined with others, also made with achromatics, by 

 Mr. Grove, Mr. Main, and Mr. Lockyer. 



These various observations, made entirely without concert, were 

 rendered comparable by a calculated reduction of each to the longi- 

 tude on Mars corresponding to the epoch of each, according to one 

 standard. [Tables of these reductions were given in the paper.] 

 The sketches were then arranged on sheets in the order of the com- 

 puted longitudes ; and, in addition, two globes were exhibited, on 

 one of which the main results of the author's observations were 

 drawn, the data for the other being supplied by Mr. Lockyer' s 

 sketches. 



He was also aided in the explanations by large drawings made 

 with reflectors by Mr. De la Rue and Mr. Nasmyth. 



* Herschel, Madler, Jacob, De la Rue and Secchi have all published careful 

 drawings of Mars. 



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