Tem'perature of the Terresirial Globe. Il 



upon this planet is evidently insensible. The temperature of the 

 surface differs therefore, very little from that of planetary spaces, or 

 from that which is observed at the poles of our globe. We have 

 made known this last result in a discourse recently delivered before 

 the Academy. It is evident we can apply it only to the most dis- 

 tant planets. We know of no means of assigning with any precision 

 the mean temperature of the other planetary bodies. The motion 

 of the air and waters, the extent of tlie seas, the elevation and form 

 of the surface, the effects of human industry and all the accidental 

 changes of the earth's surface, modify the temperatures of each cli- 

 mate. The character of phenomena attributable to general causes 

 exists : but the thermometrical effects observed at the surface are 

 different from what they would be without the influence of accessory 

 causes. 



The motion of the waters and of the air, tends to modify the ef- 

 fects of heat and cold. 



It renders their distribution more uniform, but it would be impos- 

 sible for the atmosphere to supply the place of that universal cause 

 which supports the common temperature of the planetary spaces ; 

 and if this cause did not exist, we should observe, notwithstanding 

 the atmosphere and seas, an enormous difference between the tem- 

 peratures of the equatorial and polar regions. 



It is difficult to know how far the atmosphere influences the mean 

 temperature of the globe ; and in this examination we are no longer 

 guided by a regular mathematical theory. It is to the celebrated 

 traveller, M. de Saussure, that we are indebted for a capital experi- 

 ment, which appears to throw some light on this question. 



The experiment consists in exposing to the rays of the sun, a 

 vessel covered with one or more plates of glass, very transparent, 

 and placed at some distance one above the other. The interior of 

 the vessel is furnished with a thick covering of black cork, yjroper 

 for receiving and preserving heat. The heated air is contained in 

 all parts, both in the interior of the vessel and in the spaces between 

 the plates. Thermometers placed in the vessel itself and in the 

 intervals above, mark the degree of heat in each space. This in- 

 strument was placed in the sun about noon, and the thermometer in 

 the vessel was seen to rise to 70°, 80'°, 100°, 110°, (Reaumur,) 

 and upwards. The thermometers placed in the intervals between 

 the glass plates indicated much lower degrees of heat, and the heat 

 decreased from the bottom of the vessel to the highest interval. 



