NATURAL PHILOSOPHY. 157 



rature in any latitude is found to be nearly the same in amount for the 

 terrestrial surface and for the part of the atmosphere resting upon it. This 

 must be understood as applying to those places at which the temperature is 

 not materially affected by the horizontal transference of heat by marine or 

 aerial currents, or any local causes, which disturb the dependence of tempe- 

 rature on latitude alone. 



The author also points out the dependence of the annual inequalities of the 

 terrestrial temperature (and consequently of those also of the atmosphere) on 

 the conductivity and specific heat of the matter wlrich constitutes the earth's 

 crust. 



If these were much greater, the annual changes of temperature would be 

 much less. Before applying these results to other planets, the author states 

 that he does not admit the notion, that the remoter planets may derive a con- 

 siderable superficial temperature from the remains of that internal heat which 

 they probably possessed in the earlier stages of their existence. It is a weh 1 

 established conclusion, that the superficial temperature of our own globe has 

 arrived at that point below which it can never descend by more than the 

 small fraction of a degree, so long as all external conditions remain the same 

 as at present ; and the superficial temperature of the remoter planets will in 

 ah 1 probability be reduced to the corresponding limit. To these external con- 

 ditions, therefore, and not to their primitive heat, must the existing tempera- 

 tures on the surface of these planets be attributed, assuming always that they 

 are not of less antiquity than our own globe. Hence the superficial tempera- 

 ture of the earth, with its present atmosphere, placed at the distance of 

 Neptune, Uranus, or Saturn, would be very nearly 39. 5 C., since the effect 

 of our solar radiation at those distances would be nearly insensible. But if the 

 extent of the atmosphere were increased the superficial temperature would 

 be augmented in a corresponding degree. Judging by the decrements of 

 temperature observed by Mr. Welsh, the author concludes that an increase in 

 the height of the earth's atmosphere of 35,000 or 40,000 feet, would elevate 

 her superficial temperature, if placed in the remote planetary regions, to 

 nearly the mean temperature of our present temperate zone. The same con- 

 clusion will hold with respect to the three planets above mentioned, if we 

 suppose them to have atmospheres similar to that of the earth, and of suffi- 

 cient extent. Their temperatures must be sensibly uniform over the whole 

 of their surfaces, not being subject to any appreciable annual variation. 



The same conclusions will apply to Jupiter, except that there will be a 

 small augmentation of temperature arising from solar radiation, which the 

 author calculates might amount to about 2|- C. at his equator. Hence, the 

 author concludes, that those views which assign a necessarily low temperature 

 to the above mentioned planets, in consequence of their distance from the sun, 

 are altogether untenable. 



The conditions under which Mars is placed approximate more nearly to 

 those of the earth than for any other planet. The author calculates, that 

 with an atmosphere similar to that of the earth, and exceeding it in height by 

 about 15,000 or 20,000 feet, the equatorial temperature of Mars may be about 

 60 P.. or 15 C., and his polar temperature about 10 C. The extent of the 



