ASTRONOMY AND METEOROLOGY. 327 



much intenser, while it is summer heat in the valleys below. Accord- 

 ingly, if the Martial atmosphere be only slightly denser than our own, 

 the diminution in intensity would be in great measure compensated. 

 So much for a priori reasoning. Now what is the fact ? The polar 

 snows of Mars can be distinctly seen. A white spot of excessive brill- 

 iancy at the pole, which diminishes as the summer draws on, and en- 

 larges again with winter, has been observed by many astronomers in 

 Mars. How is this compatible with water's freezing at its equator and 

 alcohol at its temperate zone ? Mr. Lockyer watched the south pole 

 of Mars throughout last autumn. Early in August, the southern hem- 

 isphere of Mars would be entering on the season which corresponds 

 with us to our May. In about a month's time, between August and 

 September, he saw the white spot at the southern pole of Mars dwindle 

 from about twenty degrees to ten degrees. In other words, the snow 

 melted for that this phenomenon is caused by the melting of the 

 snow is scarcely doubted from about eighty degrees south latitude 

 up to ninety degrees south latitude, as the summer heat came on. The 

 white spot was stationary, if not beginning to extend again before the 

 observations ceased, nearly three months after the polar snow had be- 

 gun to dwindle. This is a very remarkable confirmation and even ex- 

 tension of Beer and Madler's observations. They noted the decrease, 

 but no decrease so rapid as that observed by Mr. Lockyer. 



Mr. Lockyer's observations are also very interesting on the forms of 

 what we may fairly call the oceans and inland seas of the southern 

 hemisphere and equatorial regions of Mars. The observations are so 

 clearly defined, and agree so well in general outline with all that have 

 been made for the last thirty years that it is at least quite certain 

 that they are permanent features of the planet, and not merely bands 

 of clouds. It is assumed that the permanent dark surfaces many 

 of which, of exceedingly remarkable shapes, have now been verified 

 again and again by successive observers represent either seas, or 

 permanent rifts and chasms in the planet, seas, of course, being 

 much the more likely, while the brighter regions indicate the more 

 perfect reflection of light from the surface of continents or land, 

 the permanently dazzling spots being confined to the polar snows. If 

 this be so, we can assert that several very remarkable seas including 

 inland seas, some of them connected and some not connected by straits 

 with still larger seas are now defined in the southern hemisphere, in 

 which (as is the case also with the Earth) water seems to be much 

 more widely spread than in the northern hemisphere. There is, for 

 example, a southern sea exceedingly like our Baltic in shape. And 

 there is another and still more remarkable sea, now defined by the ob- 

 servations of many successive observers, near the equator, a long strag- 

 gling arm, twisting almost in the shape of an S laid on its back from 

 east'to west, which is at least a thousand miles in length and a hun- 

 dred in breadth, as if a channel as wide as that between England and 

 Ireland existed in equatorial Africa, and ran inland for a thousand 

 miles or more. The masses of land in Mars appear to be less unbroken 

 in the northern hemisphere ; but it is long since we have had any 

 good opportunity of observing the northern hemisphere of Mars, as its 

 year is so nearly equivalent to two earthly years that it continually 

 returns into proximity with the Earth, with the same southern pole 



