Aerial Naiigatlorii 83 



uertson with a large sail, which served to guide his wav ; 

 but as this sail would have shaken his balloon too inuchj he 

 fastened it to a smaller oiiei the inotion oF which was inde- 

 pendent of that of the other. By these means he was 

 enabled to direct his balloon in an oblique line, fifteen 

 degrees different from that in \\ hich he would have been 

 conducted by the wind. Professor Robertson observed, that 

 the atmospheric electricity suddenly disappeared as often as 

 he moved over a forest, though the sky was serene, and 

 though at other times it always gave strong and abundant 

 signs of its existence. About three quarters past five he 

 had attained to his greatest height, namely 700 fathoms ; 

 the thermometer then stood at six degrees above zero. 

 About six o'clock the Professor descended in a plain, near 

 the forest of Tresdorf, to the north of Kronenburg, at the 

 distance of four leagues and a hall' from Vienna. The bal- 

 loon hovered a long time over the plain, because the anchor 

 which was thrown out did not find a sufficient hold in the 

 new-lilled land ; ^nd as the Professor observed that he was. 

 about to be driven against two large trees which stood in 

 his way, he threw the extremity of his sail Against the 

 earth, and, in consequence of the shock it produced, rose 

 over the trees, which then caught the anchor and stopped 

 the balloon. M. Robertson here obtained every assistance 

 from the surveyor M. Octtl and M.Bartsch,wh() were here 

 hunting. Yesterday morning he returned hither about 

 eight o clock in a carriage attended by the populace, and 

 entered the city amidst loud acclamation;;. 



By M. Gmj^Lussac. 



M. Gay-Lussac has given the followinsr account of his 

 last* aerostatic ascent, to the first class ot the Narional In- 

 stitute. 



He ascended on the 6th of September at ten in the morn- 

 ing, from the Jardin du Cojiscrvatoire des Arts et Metiers, 

 which is about 20 toiscs higher than the level of the sea. 

 His barometer then stood at 2b in. 3-33 lines, and the mer- 

 curial centigrade thermometer indicated in the shade 27-75 

 degrees. These two instruments varied very little at tlie 

 earth, orduring the course of the ascension, and their changes 

 were observed every hour by M. Bouvavd at the Ooser- 

 v^tory. M. Gay-Lussac in ascendino- made a great many 

 observations on the barometer, the thermometer, the hy- 

 grometer and the magnetic needle. ' ' 



^ For an account of liis forinf r T:r-eiir sec our la';t N'Jinbir. 



r 2 At 



