MARS AS A WORLD, 161 



moderate telescopes, that it should obviously be adopted 

 as the zero from which all longitudes should be measured. 

 The nomenclature of the different objects is a little con- 

 fusing. The zero of the longitudes was called the Oculus 

 by Madler, the Terby Sea by Green, and the Lacus Solis 

 by Schiaparelli. The zero now mentioned is not that 

 which Mr. Green had employed. Professor Schiaparelli, 

 in his charts of the appearance of Mars in 1881-82, places 

 the meridian of 90 through what he has called the Lacus 

 Solis, and which, following Mr. Knobel, is the zero of 

 longitudes. The Oculus or the Lacus Solis, or the Terby 

 Sea, whichever name be adopted, is to be regarded as the 

 Greenwich on the planet Mars. In my " Atlas of Astro- 

 nomy " I have given a map of Mars, in which the nomen- 

 clature has been determined from a careful comparison 

 of the different authorities. 



Mr. Green has provided us with an excellent reason for 

 referring to his picture of Mars on September 10th. He 

 tells us that it " was without comparison the grandest 

 obtained at Madeira. This drawing also, of all the series, 

 most effectually recalls the impression made at the tele- 

 scope ; this sight of Mars was felt at the time to be a rich 

 reward for every effort, and will remain, while memory 

 lasts, a constant delight and satisfaction." 



The interpretation of the various marks which pictures 

 of the planet exhibit involves questions that must still 

 be regarded as of a somewhat speculative character. It is 

 so natural for us to conjecture that the objects on the 

 planet may be of identical nature with the objects on the 

 earth, that we are accustomed to employ language on the 

 subject that is apt to express more than the extent of our 



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