5# VVEROSTATIC VOYAGE. 



Problem for Gitefi' the temperature on the earth and m the car, the 



>XcUy of 1^* height of the barometrical cohjmn, and the time employed in 

 talioon by obf. the apparent tranfit of an objed on the earth through a given 



(fcTc?^ ^ ^^^^' *"^'^ ^^ ^^^^ '^^ '''^"^^ ^^ fi"^ ^^^ velocity of the obferver. 

 Tabulated refults Forpra61ice it would perhaps be fufficiently exad and con» 

 for praaiec venient to compute a fraall table, in which, negleding the tem-» 

 perature, the velocity in miles per hour might be had by in- 

 fpeclion, when the height of the mercury, the time of tranfit, 

 and the magnifying power were known. 

 The obfervfd The aeronauts having noticed by their inftruments what 

 courfe, &c. nfere thie direction of the currents of air at.ditierent heights, 

 found themfelves in one which carried them directly to-.vards 

 the Baltic. They therefore defcended till they fg.w by tiie ba- 

 rometer that they had returned to a current which carried them 

 inland; and afterwards again rofe much higher, and faw witli 

 gredt precilion by their telefcope the initant of their quitting 

 A pigeon let the gulph. When the barometer Hood at 24 inches they let 

 fi*^* go a pigeon, who flew with duTiculty and would not quit the 



balloon; but upon being precipitated he in vain endeavoured 

 to regain it, and at length defcended rapidly towards the earth. 

 The dip of the ^t ten at night the balloon had rifen to an height indicated by 

 magnetic needle ^g inches of the mercurial column, tiie thermometer ftandinjr 



js lets at great • - ' . . *^ 



heights in die at 4|- degrees (I fuppole centigrade). Here it was that M, 



^^^f Sachatoff carefully obferved a phenomenon which had been 



before remarked by M. Robertfon in his afcent from Hamburgh, 



but at a much greater elevation. Their dipping needle was 



deranged; but on. infpefling the common compafs, its needle 



was found to be no longer horizontal, the north end being 



This may afford elevated near 10 degrees. On this phenomenon they remark 



■""^tb °heiTts ^^^^ ^^^ magnetic attraction probably diminifhing as thefquare 



&c, of the diftance may afrord additional means of dired^ing future 



obfervers in theatmofphere, and even determine the elevations 



independently of the barometer. F'om the prefent elevation 



a pigeon being thrown down, tell fo diredtly th^t it was doubted 



whether he could have reached the earth alive. 



Singular echo Darknefs coming on, it became neceflary todefcend, during 



of the voice which the obferver repeatedly made an experiment which alfo 



parth at the dif- pJ'OHO'^^s to be of great utility to voyagers in the air, ^s well as 



tancc of two lo enlighten our conclufions refpedfing the phenomena of 



^^^'" found. When ihey fpoke through a trumpet directed towards 



thp earthy the voice was returqed with extreme precifion an4 



VvithpiJt 



