1865.] Phillips on the Planet Mars. 377 



On the whole then, the circumstances already collected regarding 

 the physical aspect of Mars appear to justify the conclusion, that the 

 planet has a larger proportion of land than water, in this respect dif- 

 fering from the earth, and that the land is mostly collected in a broad 

 band, including the intertropical spaces, and the north temperate 

 region, while broad seas encircle the north pole and a large proportion 

 of the south temperate zone. In this last-mentioned large space, the 

 appearances vary much, and in such a manner, as to indicate the 

 overspreading of clouds, which reflect much light, and leave visi- 

 ble between their vaporous masses, the darker surface of the sea. 

 Some particular limited tracts, of sea channel apparently, much 

 darker than the rest of the surface, may, perhaps, derive this hue 

 from greater depth of water. We are thus placed by telescopic 

 observation in front of a planet, whose main characters of surface 

 correspond to those of our earth ; which has nearly the same density ; 

 nearly the same daily and nightly period ; and is enveloped like our 

 earth, by an atmosphere partially loaded with scattered clouds. It 

 has also a character of climate not much different from the more 

 continental parts of our globe, with which, on account of the excess 

 of land over water in Mars it may be most fairly compared. How is 

 this character of climate obtained by Mars, while the mean quantity of 

 sunshine falling on any particular tract is only (rinr) 2 of that which 

 reaches and warms the earth ? Only two suppositions can be at all worthy 

 consideration : the flow of heat from the interior of Mars may be 

 greater than in the earth, and the waste of heat from the surface may 

 be much less. These may co-exist ; but the most important, beyond 

 any doubt, is the second. The waste of heat from the earth's surface 

 would be enormously greater, and very much more rapid, than it is, 

 but for the atmosphere, which acts in two ways to prevent it. 

 First, it acts like a coating to a steam-pipe— the more of it the 

 greater the effect. A greater depth of atmosphere round the earth 

 would keep it very much warmer. If we suppose the effect to be 

 proportional to the density (or pressure), then twice as deep an 

 atmosphere as that which exists round the earth would sensibly 

 raise the temperature, and in the same way the same effect would 

 be produced in Mars. Again, the atmosphere has a specific action 

 of this kind — it permits the solar light and heat to pass to the 

 earth, yet by reason of its peculiar constitution, especially by the 

 aqueous vapour and watery particles suspended in it, obstructs the 

 radiation of heat from the earth. If, then, we suppose the atmo- 

 sphere of Mars to be deeper than that of the earth, the waste of 

 heat will be less.* It cannot contain more aqueous vapour, in pro- 

 portion, than the earth, unless there be warmer oceans on Mars, for 

 its marine area is less ; but with a greater depth of atmosphere the 



* " If we allow to Mars an atmosphere similar to that of the earth, but of 

 greater thickness, to the amount of some 15,000 or 20,000 feet, the mean tempera- 

 ture may be 60° Fabr. at the equator and about 14° or 15° Fahr. at the pole, 

 supposing the additional atmosphere to have rather less effect at the pole than at 

 the equator." — Hopkins in ' Camb. Phil. Trans' 1855, p. 663. 



