AEROSTATIC VOYAGE. !279 



meridian with facility. M. Coulomb, after having touched 

 the needle, proved it by the method which he propofed in the 

 Memoirs of the Inftitute; and he found that it gave an incli- 

 nation of 70.5° of the common fcale. In one of it^ pofitions, 

 which was that in which it was to remain, it varied 31°. 



In our firft afcenr, the under furface of the glafs which Azimuth com- 

 covered our azimuth-compafs was covered with water, and pas " 

 we were prevented from feeing the fiiadow of a horizontal 

 thread, which ferved us for a ilyle. To avoid this inconve- 

 nience, it was fuffkient to remove the glafs of the compafs ; 

 in other refpe&s, no alteration was made in its firft difpofition. 

 M. Lepine again fupplied us with two fecond-watches, one 

 of which was a flop-watch : it was with the latter that I made 

 all my obfervations. 



The thermometer I uTed, was the centigrade mercurial Thermometer, 

 thermometer. To guard it from the aclion of the fun, we 

 placed it within two concentric cylinders of pafleboard co- 

 vered with gilt paper, one of which was about four centi- 

 metres in diameter, and the other fix. Our hygrometers Hygrometers, 

 with four hairs, of the conftruclion of M. Richer, were dif- 

 poled in nearly a fimilar manner. The two glafs balloons in 

 which I was to bring the air, were exhaufted lo nearly a milli- 

 metre of mercury, and we were fatisfied by leaving them in 

 this ftate for eight days, that they perfectly retained the va- 

 cuum. For fear of an accident, we had provided a third bal- 

 loon of brafs ; but very fortunately it was ufelefs. 



Our two barometers have not a conflant level ; and to ge! Barometers; 

 the true barometric heights, we formed a table of companion, 

 by placing them under the receiver of the pneumatic ma- 

 chine, and rneafuring their depreffion from five to i\ve cen- 

 timetres, by means of a ftandard, the refervoir of which has a 

 con'tant level, and which is provided with a very good fcale. 

 Being no longer obliged to obferve more than the upper level 

 to get the true barometric heights, the number of obfervations 

 was diminifhed to one half ; which is of great importance when 

 the attention is divided between perfonal iafety and delicate 

 experiments. 



Such nearly were the effential inftruments I took with me 

 in my voyage. I was alfo provided with an apparatus foi The apparatus 

 determining the electricity of the air ; but a few moments after fov meafu "ng 

 t ■• i f , ti n i ii- j - , • . rheeiedricityof 



1 quitted the earth, I loit the two metallic wires which weie the air rendered 



to 



ufelefs. 



