June 24, 1898.] 



SCIENCE. 



847 



for observations ■witMn. a mile or two of the 

 earth, the captive kite-balloon and kites 

 with self-recording instruments. Aside 

 from technical details, the most important 

 decisions concerning balloons related to the 

 measurements of their height and of the 

 air temperature around them. Although, 

 for the determination of height, from ob- 

 servations in the balloon, the mercurial 

 barometer must be considered as the stand- 

 ard, yet its indications are only accurate 

 when the balloon has no vertical veloc- 

 ity. If aneroids are used they should be 

 ■compared frequentlj' with the standai'd and, 

 so far as possible, under actual conditions. 

 It was decided that for the calculation of 

 height the barometric observations should 

 be reduced everywhere by the same method, 

 whatever that might be ultimately. M. 

 Cailletet described his apparatus for pho- 

 tographing automatically, at fixed intervals 

 of time, a barometer in the balloon and the 

 ground vertically below, so that the 

 barometric heights can be calculated and 

 from a map the true heights and the route 

 of the balloon may be determined. This 

 apparatus was recommended for use with 

 both manned and unmanned balloons. On 

 account of the rapid changes of tempera- 

 ture, it was recognized that very sensitive 

 thermometers must be employed in ballons- 

 sondes and that their artificial ventilation 

 is essential. M. Cailletet exhibited a 

 thermometer having a spiral silver tube 

 for its bulb soldered to a glass tube, both 

 being filled with the liquid toluene. This 

 thermometer is extremely sensitive. M. 

 Teisserenc de Bort showed a very sensitive 

 self-recording thermometer which is at 

 the same time almost insensible to shocks. 

 It is composed of a blade of German sil- 

 ver set in a frame of invariable steel, and 

 can be ventilated in a hallon-sonde by a fan 

 turned 'by a weight attached to a long wire. 

 For the determination of the temperature 

 of the air around manned balloons the 



proper instrument to employ is Assmann's 

 aspiration thermometer, hung at least 5 

 feet outside the basket, but simultaneous 

 comparisons with the sliug thermometer 

 were advised. The self-recording instru- 

 ments carried in manned and unmanned 

 balloons should be verified in pneumatic 

 and refrigerating cabinets under such 

 changes of pressure and temperature as 

 might occur in the atmosphere. 



Drs. Hergesell and Berson urged the im- 

 portance of simultaneous balloon ascents in 

 the different countries when there was a 

 barometric depression over the European 

 continent. From a meteorological stand- 

 point the manned ascents have an impor- 

 tance which the 6a/foas-so?ides do not possess, 

 because the temperature of the highest at- 

 mosphere has no influence on the meteoro- 

 logical elements near the surface of the 

 earth. M. de Fonvielle, however, called at- 

 tention to the interest which thermometric 

 measurements at a very high altitude would 

 ofier for the determination of the tempera- 

 ture of planetary space. These measures 

 might enable us to choose between the 

 kinetic theory of gases, which assumes the 

 temperature of 273° Centigrade below zero, 

 and Fourier's hypothesis that the temper- 

 ature of space is near that of the minima 

 observed in the polar regions of the earth. 



It was agreed that the fifth international 

 ascent of ballons-sondes should take place 

 early in June, and manned or unmanned 

 ascents were promised in Austria, Belgiiim 

 and Italy, in addition to those in Germany, 

 France and Eussia, which countries had 

 already cooperated. On the day designated, 

 observations at the mountain stations, as 

 well as with kites and captive balloons, will 

 serve for the simultaneous study of the 

 lower air. 



Mr. Eotch read a report, which he had 

 been asked to prepare, on the use of kites 

 for meteorological observations, based on 

 the experiments carried on at Blue Hill Ob- 



