158 ANNUAL OF SCIENTIFIC DISCOVERY. 



annual variations would be about half those on our own planet in correspond- 

 ing latitudes, supposing the conductivity, specific heat, and radiatory power 

 of the matter composing his superficial crust to be the same as for the earth. 



Again, if the earth, with ner present atmosphere and obliquity, were placed 

 in the orbit of Venus, the mean equatorial temperature would be upwards of 

 90 C., subject to the reduction, which would doubtless in this case be great, 

 due to the horizontal transference of diminution in the atmosphere, which 

 would reduce these temperatures in any assigned degree. But the obliquity of 

 Venus, though not satisfactorily determined, is considered to be much greater 

 than that of the earth, amounting, according to the estimate of some astrono- 

 mers, to as much ag 75, as heretofore stated. 



This would, of course, render the character of her seasons entirely different 

 from those of the earth. The greatest mean annual temperature would be at 

 the pole. Independently of the horizontal transference of heat by aerial cur- 

 rents or other causes taking the extreme obliquity of 75, and supposing the 

 atmosphere of Venus to be exactly like that of the earth, her mean tempera- 

 ture at the equator would be about 56 C., and at the pole 95 C. 



This latter would probably be much lowered by currents ; but if the height 

 of the atmosphere of Venus be less than that of the earth's atmosphere by 

 25,000 feet, the author considers that the mean temperature of Venus in her 

 equatorial regions would not exceed that of the temperate regions of the 

 earth ; while the mean polar temperature would probably be about 40 C., or 

 about 12 or 13 C. higher than the earth's equatorial temperature. 



The heat of sunshine may be moderated by an atmosphere more laden 

 with vapor than that of the earth. 



Supposing the atmosphere of Venus like that of the earth in its nature and 

 magnitude, the temperature at her poles, with the supposed obliquity, must 

 be subject to an enormous annual inequality, amounting to between 70 and 80 

 C. above or below the mean temperature, liable, however, to a great reduction 

 by horizontal transference of heat. It may also be considerably reduced by 

 the nature of the matter which constitutes her outer crust. 



The moon is under the peculiar circumstances of the absence of a sensible 

 atmosphere, and her long period of rotation about her axis. Assuming her 

 to have no atmosphere at all, the mean temperature of her outer crust, 

 in the absence of the sun, would be the general temperature of that portion 

 of planetary space in which the solar system is situated. How much this 

 might differ from the superficial temperature which the earth would have with 

 the like absence of the sun, and which the author estimates at 39. 5 C., as above 

 stated, it is impossible to determine ; but whatever it may be, the influence of 

 the sun's heat would be to increase by about 40 C. at the mooivs equator, and 

 by a small amount only at her poles. This must be attended by an enormous 

 monthly inequality, amounting to nearly 60 C., supposing the matter of 

 which her superficial crust is composed to have the same conductivity, specific 

 heat, and radiating power as the crust of the earth. 



If these be much greater for the moon, this inequality might be consider- 

 ably diminished. At the poles it must be comparatively small. 



The lunar temperatures here spoken of, are those which would be indicated 



