EXPLORATIONS OF THE UPPER ATMOSPHERE. 305 



crossed threads of the instrument. Movements of the telescope in 

 the vertical and in the horizontal planes are transmitted, by means of 

 cogwheels and a chain invented by Galle, to an arm carrying a writing 

 pen. The tracing made by this pen on a sheet of cross- section paper 

 borne on a vertical cylinder gives the various angles of the balloon in 

 zenith and azimuth, and constitutes a complete diagram. In the model 

 used in the ascension of the 5th of August, 1896, the registering cylin- 

 der was 18 centimeters high and 7 in diameter, revolving in iifty-flve 

 minutes. Using cross- section paper with millimeter squares, we have, 

 for every minute of time, 4 millimeters of horizontal displacement of 

 the cylinder. For zenith distances from 0° to 90°, 1 millimeter equals 

 one-half a degree, and for azimuths, 2°. To obviate confounding the 

 tracings, the pens carry ink of different colors. 



This apparatus can not pretend to the extreme precision of the the- 

 odolites employed in geodesy, but it has the compensating advantage 

 that it furnishes a document that can be examined at leisure. With 

 two dromographs established on a suitable base, the actual height of 

 the aerostat may be determined with a certain amount of approxima- 

 tion, and this may then be compared with the registering diagrams of 

 the balloon. 



While waiting, M. Hermite has made interesting observations upon 

 the velocity and direction of winds at high altitudes, using the baro- 

 metric diagram to solve the triangle. 



Now that we have become acquainted with the apparatus employed, 

 we may consider the three last trials that have been made in France 

 with the instruments just described. 



III.— THE ASCENSION OF AUGUST 5, 1896. 



At 11.40 a. m. the Aerophile, provided with its basket protector con- 

 taining the barothermograph carrying within the balloon a registering 

 thermometer and jirovided with a 12 pound apparatus for automatic- 

 ally taking in air, was ready to start. The signal being given and 

 the mooring cord cut, the balloon darted up with great velocity, carry- 

 ing its load of instruments. The dromograph properly set up registered 

 the trajectory followed- but at 12.10 o'clock at a height of about 8,500 

 meters and at a distance of 22 kilometers from the gas works of La Yil- 

 lette, the place of departure, the Aerophile disappeared behind thick 

 clouds while still continuing its ascent. That very evening a dispatch 

 arrived at Paris announcing that the recording balloon had come to 

 the ground in Germany, at Medermiebach, about 30 kilometers beyond 

 Cologne, where M. Hermite went the next day to get it, finding the 

 apparatus in a perfect state of preservation. 



An examination of the barogram showed that the ascent was made 



with an average velocity of 6 meters per second, and that the maximum 



altitude was reached at 12.33 p, m., about three-quarters of an hour 



after the start. The barometric pressure had then fallen to about 135 



SM 97 20 



