578 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



besides those pieces that are the invariable accompaniments 

 of such expeditions, there was a Davy's lamp for illumina- 

 tion at night, two beautiful spectroscopes, and an instru- 

 ment by the aid of which it was easy to determine the ve- 

 locity of the wind that is to say, the velocity of the hori- 

 zontal movement of the balloon. Tissandier also experi- 

 mented with the aspirator to determine the quantity of 

 carbonic- acid gas. Sivel introduced, apparently for the 

 first time in French aeronautics, the guide-rope, with which 

 American readers are familiar from its usefulness in the ex- 

 pert hands of Mr. S. A. King, of Boston. The rope used by 

 Sivel was, however, some 4000 feet long, and it was intended 

 that it should generally touch the earth and glide along 

 over the soil, thus acting as a rudder to the vessel, giving a 

 certain fixed direction to the car of the balloon, and pre- 

 venting its gyration. Sounding balloons, as they were call- 

 ed, were also devised by Sivel. One of them was filled with 

 illuminating gas, the other with air, and these two balloons, 

 fixed at the end of a horizontal rod, floated one above and 

 one below the car, and always indicated the relative upper 

 and lower winds. During the night the altitude of the bal- 

 loon oscillated between 700 and 1100 meters, the tempera- 

 ture being between 1 and 4-J C. Cirri were always above 

 the balloon, increasing during the night, and giving rise to 

 a magnificent halo in the mornino; on the rising of the sun. 

 The moon was also surrounded by a similar halo. A mod- 

 erate southwest wind had been predicted from the consider- 

 ation of the weather charts, and was actually experienced, 

 replacing the northeast wind with which they started. The 

 balloon followed the prominences of the soil very exactly, 

 being pushed up over the hills by the ascending current 

 whenever it came to any elevation. This fact was especially 

 manifest in that portion of the voyage during which the al- 

 titude was but 600 meters. The balloon itself was frequent- 

 ly inclined out of the vertical. Very appreciable variations 

 in the velocity of the wind were experienced, amounting to 

 between five meters per second during the night and ten 

 meters at sunrise, and diminishing in the upper regions, con- 

 trary to the usual experience. Slight traces of electricity 

 were observed at sunrise, but not during the night. Bull. 

 Jlebcl, XVI, 33. 



