AERONAUTIC VOYAGES. 343 



than Gay Lussac had ascended. It is proper to observe that the formulas used 

 In calculating heights proceed upon the hypothesis of a nearly vmiform decrease 

 of temperature, and that, in this instance, a change of elevation which may be 

 estimated at 600 meters, was attended by a variation of temperature of about 

 30 degrees, Avhile, in an unclouded atmosphere, the variation would have been 

 but from 4 to 5 degrees. 



" The important discovery made in this aeronautic voyage shows what science 

 may expect from like expeditions when they shall be confided, as at that time, 

 to intrepid, careful, exact, and candid observers." 



The following is an extract from the journal kept by the two accomplished 

 physicists during the voyage : 



"The graduated instruments which we carried with us had been constructed 

 by M. Fastre, under the direction of M. Regnault. The tables of graduation 

 had been prepared in the laboratory of the College of France, and were known 

 only to the last mentioned-savant. 



" The balloon is the same which served for our first ascension ; it is formed 

 of two hemispheres of a radius of 4.8 millimeter, separated by a cylinder 3.8 

 millimeter in height, having for its base a great circle of the sphere. The total 

 volume of the balloon is 729 cubic meters. A lower orifice, intended to give 

 issue to the gas during its dilatation, is terminated by a cylindrical appendage of 

 silk, 7 meters long, which is left open to permit the free escape of the gas dur- 

 ing the period of ascent. The car is suspended at about 4 meters below the 

 orifice of the appendage, so that the balloon may float at the distance of 11 

 meters from the car, and in no respect iuterfere with the observations. The 

 instruments are fixed around a large cast-iron ring which is attached to the 

 usual wooden circle for securing the cords of the car, and is of such a form 

 that the instruments may be within convenient distance of the observers. 



"It was our intention to set out at about 10 o'clock a. m., and measures had 

 been taken for commencing the inflation of the balloon, an operation with which 

 MM. Veron and Fontaine were charged, at 6 o'clock. Unfortunately, circum- 

 stances beyond our control, and arising from the necessity of thoroughly wash- 

 ing the gas in order to guard against its action upon the tissue of the balloon, 

 occasioned delay, and it was 1 o'clock before the arrangements were completed. 

 The sky, which had been quite clear tdl noon, became covered with clouds, 

 and soon a deluge of rain was falling upon Paris. This continued until 3 o'clock. 

 The day was then too far advanced, and the condition of the atmosphere too 

 unfavorable, for us to hope that we could carry out the programme wc had pro- 

 posed. But the aerostat was ready, great expense had been incurred, and it 

 was possible that observations in this troubled state of the atmosphere might 

 lead to useful results. We decided, therefore, to ascend. Our departure took 

 place at 4 o'clock. Some difficulty was occasipned by the narrowness of the 

 space which the garden of the observatory aftorded for the evolution of ascent. 

 The balloon, as has been seen, was at a considerable distance from the car, and, 

 swept forward by the wind, got the start of the frail skiff in which we were 

 embarked, so that it was only through a series of oscillations, sufficiently 

 divergent on either side from a vertical line, that we attained a state of tranquil 

 suspension from the aerostat. We came in contact with trees and a pole, by 

 which one of the barometers and the thermometer with a blackened surface 

 were broken, and these were left behind. We shall here transcribe the notes 

 taken during our ascension. 



" 4^' 3*". Departure. — The balloon ascends at first slowly, taking a direction 

 towards the east. The movement of ascension becomes more rapid after the 

 discharge of some kilograms of ballast. The sky is completely covered with 

 clouds, and we presently find ourselves in a light mist. 



