Geological Society. 325 



atmosphere round the earth would greatly exaggerate the difference of 

 daily and nightly, and of winter and summer temperature, so the con- 

 trary effect would follow from an augmentation of it. Applying this 

 to Mars, we shall see that his extensive atmosphere would reduce 

 the range of summer and winter, and of daily and nightly tempera- 

 ture. It would, moreover, augment the mean temperature by the 

 peculiar action of such an atmosphere, which, while readily giving 

 passage to the solar rays, would resist the return of dark heat-rays 

 from the terrestrial surface, and prevent their wasteful emission 

 into space*. This effect obtains now on the earth, which is ren- 

 dered warmer, as well as more equable in temperature, by the atmo- 

 sphere than it would be without it. It is conceivable that it may 

 obtain upon Mars to a greater degree, even without supposing the 

 atmosphere to be materially different in its nature from that round 

 the earth, or the surface of Mars to have any specially favourable 

 or exceptional characters for the absorption and radiation of heat. 

 It seems, however, requisite to suppose a greater communication of 

 heat from the interior of the planet ; for otherwise the additional 

 vapour, to which the warming effect is in the main to be ascribed, 

 could not probably be supported in the atmosphere. On the whole 

 we may, perhaps, be allowed to believe that Mars is habitable. 



Here, so far as direct observations upon the aspect of Mars are 

 available, we may pause. The researches of the Rad cliff e Observer, 

 lately in Oxford, and formerly at Greenwich, have, however, brought 

 into view a peculiarity in the constitution of this planet which deserves 

 special notice. Its figure is spheroidal, as might be expected from 

 the general laws of planetary form ; but it is spheroidal in so high 

 a degree as to be quite exceptional in this respect. Computing 

 by the known rotation-velocity, and the admitted measures and 

 mass of Mars, its ellipticity should be about -^ho m ^ r - Mam's 

 observations with the splendid Oxford Heliometer give as the most 

 probable result, the large fraction of ^^ for 1862. This excellent 

 astronomer has continued his observations during the late opposition. 

 My own attempts to obtain the ellipticity with the micrometer eye- 

 piece reading to 0" # 2 of arc failed to give satisfactory measures. The 

 ellipticity, indeed, seemed to be small, and was merely observable, 

 not really measurable or even to be approximately estimated by the 

 help of this apparatus. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 241.] 

 January 11, 1865.— Sir R. I. Murchison, Vice-President, 

 in the Chair. 

 The following communications were read : — - 

 1 . " On the Lias Outliers at Knowle and Wootton Waven in 

 South Warwickshire." By the Rev. P. B. Brodie, M.A., F.G.S'. 

 The author gave a description of the Liassic outliers at Knowle 



* Life on the Earth, 1860, p. 163-65. Tyndall's Researches, Proceedings of 

 the Royal Society, February 1861. 



