225-^ AEROSTATIC VOYAGE. 



made my obfervations, the height of the barometer on the 

 earth has been taken at "6.568 centimetres, which was the 

 cafe at three o'clock; a height which, conformably to the 

 obfervations made by M. Bouvard at the Obfervatory, is 

 greater by 0.43 millimetres than that which had been obferved 

 at the moment of my departure. The heights of the baro- 

 meter in the atmofphere have been brought to thofe which 

 would have been indicated by a barometer with an uniform 

 level placed in the fame circumflances, and the mean between 

 the obfervations of the two barometers has been taken for 

 and of the tern- each height. The temperature on the earth having alfo va- 

 perature. r j ec j yerv jj U ] e b etween ten and t j uee ,ty O qk t j t has been 



fuppofed conftant and equal to 30.75° of the centigrade ther- 

 mometer., 

 The irregular Now on looking into the table it will be evident, in the 



temw«"ire the firft P ,ace ' that lhe temperature follows an irregular courfe 

 ari/es from the with refpect to correfponding heights; which, no doubt, is 



change of place occasioned by the obfervations having been made fometimes 

 duru-.g the ob- . r .. ' , - . . " ' ' ,. .. 



fcrvation. in alcending, and lometimes in delcending, and the thermo- 



meter having followed thefe variations loo ilowly. But if the 

 degrees of the thermometer alone are conhdered, which form 

 with each other a continually decreafing feries, a more regii- 

 DifFerenceof lar law will be found. Thus the temperature on the earth 

 elevation corre- bej 2 7.75°, and 8.5° at the height of 3691 metres, if the 



fpondingto ade- ° ° 



gree of the dif- difference of the heights is divided by that of the tempera- 

 ference of tern- i ures , we (hall at once obtain 191.7 metres (627.8175 feet) 

 of elevation for each degree of the reduction of the tempera- 

 ture. By performing the fame operation for the temperatures 

 5.25° and 0.5°, as well as for ihofe of 0° and —9.5°, we 

 flialkfind, in both cafes, 14-1.6 metres (4-63.74 feet) of ele- 

 vation for each degree of the reduction of the temperature: 

 which feems to indicate that near the furface of the earth the 

 heat is governed by a law which decreales lefs than at an 

 elevation in the atmofphere, and that at length it follows a 

 decreafing arithmetical progreffion. If it be fuppofed that 

 from the furface of the earth, where the thermometer was at 

 30.75° to the height of 6977 metres (22849.675 feet), where 

 it had fallen to —9.5°, the heat had diminished as the eleva- 

 tions increafed, an elevation of 173.3 metres (567.557 feet) 

 will correfpond to each degree of the redudion of the tempe- 

 rature. 



The 



