Mr. Hopkins on the External Temperature of the Earth. 403 



the Earth, amounting, according to the estimate of some astronomers, 

 to as much as 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 

 currents or other causes, taking the extreme obliquity of 75°, and sup- 

 posing the atmosphere of Venus to be exactly like that of the Earth, 

 her mean temperature 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 about 25,000 feet, the author con- 

 siders 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 vapour than that of the Earth. 



Supposing the atmosphere of Venus like that of the Earth in its 

 nature and its magnitude, the temperature at her poles, with the 

 supposed obliquity, must be subject to an enormous wwwwa/ inequality, 

 amounting to between 70° and 80° C. above or below the mean tem- 

 perature, liable, however, to a great reduction by horizontal trans- 

 ference of heat. It may also be considerably reduced by the nature 

 of the matter which constitutes her outer crust. A reduction, like- 

 wise, in the extent of her atmosphere, like that above supposed, 

 would probably diminish the amount of this inequality, as well as 

 the mean temperature, though not in the same degree. It is easy 

 to conceive that the coefficient of the inequality may be thus reduced 

 to some 40° C. ; and supposing the mean temperature then, as above 

 estimated, at about 40° C, the annual polar temperature will oscil- 

 late between 0° C. and 80° C. At the equator, the semi-annual in- 

 equality might amount, under the above suppositions, to about 10° 

 or 12° C, in which case the equatorial temperature might oscillate 

 between something below zero (C.) and some 25° C. It should be 

 recollected also, that a much greater reduction of the mean tempera- 

 ture would result from a greater reduction in the extent of this 

 planet's atmosphere than above supposed with reference to the height 

 of our own atmosphere. This would not, the author conceives, be 

 inconsistent with the existence of a large quantity of vapour in the 

 atmosphere, affording shelter from the heat and glare of sunshine. 



The Moon is under the peculiar circumstances of the absence 

 of a sensible atmos^'here, and her long period of rotation about her 

 axis. Assuming her to have no atmosphere at all, the mean tem- 

 perature of her outer crust, in the absence of the Sun, would be the 

 general temperature of that jjortion 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 it by about 

 40° C. at the Moon's equator, and by a small amount only at her 



