EXPLORATIONS OF THE UPPER ATMOSPHERE. 303 



spite of its light weight of 5 kilograms. Its total resistance, which 

 was 5,500 kilograms at the top, was 8,300 kilograms at the equator, 

 and thence diminished to the 8 suspension cords, which had a total 

 resistance of 4,500 kilograms. These cords were united below in a 

 single point by means of a special apparatus called a cone. It is at 

 this point of union that are fixed, first, a 'thimble in which slides the 

 cable serving to manage the balloon; then two cords, one light, at the 

 end of which the registering apparatus is suspended, the other strong, 

 to which is attached a tray charged with ballast when the balloon has 

 mounted to the desired height by the running out of the controlling 

 cable. When it is wished to let the aerostat go, one end of the cable 

 is pulled; then, when it has fallen to the ground, it is suflflcient to cut 

 with a knife the cordage that holds it. By this means there is avoided 

 all shock to the instruments, which, in the first experiments, were con- 

 siderably injured. 



The complete apparatus weighs only 41 kilograms, the same as does 

 the German balloon of 250 cubic meters, the Cirrus, mentioned above. 

 A simple calculation shows that this balloon, filled with pure hydrogen 

 having a weight of 1,150 grams per cubic meter, ought to rise to a 

 height of more than 20 kilometers. Still it has not reached anything 

 like that height, but this fact is explained when we learn that it has 

 only been filled with illuminating gas, having a lifting power of only 

 700 grams per meter, and that it has always been loaded with from 

 10 to 25 kilograms of registering apparatus. Besides, we may doubt 

 whether the formula of Laplace, by which barometers are graduated, 

 can still be applied to those regions of our atmosphere in which the 

 pressure is reduced to a few centimeters of mercury. 



II. — THE INSTRUMENTS. 



The experience had by MM. Hermite and Besangon at the time of their 

 previous trials with their Aerophile of gold-beater's skin led, them to 

 modify considerably the arrangement of the instruments carried by the 

 recording balloon, so as to make the diagrams more accurate. 



The principal record desired was that of the temperature of the 

 regions traversed, and for this purpose a registering apparatus was 

 constructed by M. Richard and tested in the frigorific chamber of M. 

 de la Baume-Pluvinel. This instrument, made almost entirely of alumi- 

 num, weighs only about 1,200 grams, and gives three different diagrams; 

 that of variations of pressure (barometer), of temperature (thermome- 

 ter), and of degree of humidity (hygrometer). The tracing is made 

 upon paper ribbons covered with lampblack, fixed on a revolving cylin- 

 der driven by clockwork. This barothermograph, when set up, is sus- 

 pended in a loosely woven wicker basket by rubber bands, thus guarding 

 the instrument from injury during the shock of landing. This basket 

 is itself hung in the same manner within a large wicker cylinder cov- 

 ered externally with silvered paper. In this way the barothermograph 

 is completely protected from solar radiation as well as from shocks. 



