278" AEROSTATIC VOVAGE. 



XII. 



Account of an Aerofiatic Voyage, made by M. Gay-Lussac 

 on the 29th Frvcildor, in the Year 12. Read to the ^National 

 lnfiitute, on the 9th Vende/niaire, in the Year 13.* 



Motives of the J-N the account of the firft aeroftatic voyage which M. Biot 

 »frent. an( j j | iac j t ^ e honour to fubmit to the Inftitute, we announced 



thai, from the furface of the earth to the height of 3977 metres 

 (J 3024.675 feet), the magnetic power did not experience any 

 fenfible diminution; and at the fame time we fignified a defiie 

 to undertake new a ("cents, to afcertain this important fact at 

 greater heights. We foon found that this was alfo the will) of 

 many members of the Inftitute; and, encouraged by the ge- 

 neral intereft which our fir ft voyage had excited, we refolved 

 on making a fecond very fhortly ; but our aeroftat not being 

 capable of carrying us together to a greater height than in our 

 firft afeent, it was agreed between us that I fliould go alone. 

 From this moment all our attention was given to the inftru- 

 ments which it was requifite for me to carry; and their con- 

 struction, wtiich was again entrufted to M. Fortin, as well as 

 an operation which the balloon underwent to give it more 

 levity, retarded my departure till the 29th of laft Fructidor. 

 Conftruaion of Inftructed by the experience of our former afeent, we 

 m rumen.s. mac j e f ome changes ill our instruments ; and, in the firft place, 

 Horizontal that the ofcillations of the horizontal needle might be lefs 



needle. affected by the rotation of the balloon, we caufed a new one 



to be constructed, only 15 centimetres in length. Thus, its 

 ofcillations being more rapid than thofe of the balloon, it 

 would be eaft'-r to determine their duration. 

 Pipping needle. We made greater modifications in die dipping needle. That 

 we might not be obliged, at each obfervation, to replace it 

 in the magnetic meridian, and to adjuft its axis truly horizon- 

 tal, we fufpended the metallic chape which fupports it by a 

 filken thread ; and, to judge of its inclination, we fixed a 

 portion of a tranfparent circle, graduated in divifions, to the 

 chape. The whole apparatus was very light, the tenfion on 

 the lilk thread but trifling, and the needle could refume its 



* Frgm Amiales de Chimie, No. 154, Fm&idor, An. XIII, 



meridian 



