August i8, 1898] 



NA TURE 



381 



St. Petersburg, and Rotch of Boston, U.S A. Regrets were 

 sent to Messrs. Hermite and Violle, whom illness detained, 

 and thanks were tendered to those governnients and friends of 

 science who proposed to search for Andre, a member of the 

 committee. A number of physicists, meteorologists, and 

 aeronauts were present as guests. The welcome of the German 

 Government was extended by Von Schraut, Minister of Finance 

 for Alsace-Loraine, who summarised the results achieved in 

 exploring the atmosphere, and predicted a brilliant future. 

 Prof. Windelband, Rector of the University of Strassburg, em- 

 phasised the importance of these researches for the progress of 

 humanity as well as for science. M. de Fonvielle replied for 

 the Committee. 



The discussion of the provisional programme was then begun, 

 with the questions relating to the hallotts sondes. It was agreed 

 that the introduction of a mechanical ballast discharger was 

 necessary, and that all precautions should be taken to prevent 

 derangement of the instruments ; the stoppage of the clockwork 

 was attributed to the contraction of the plates carrying the 

 pivots, from the effect of great cold. As regards the calculation 

 of the ascensional force of balloons and the influence of the 

 temperature of the gas, it was resolved that — 



For each unmanned ascent the weight of the aerostatic 

 material and the ascensional force at the start should be 

 measured, and during the whole voyage the true temperature 

 of the gas should be recorded. 



Since the study of the meteorological conditions of the air in 

 a vertical line is important it was considered advisable, in certain 

 ca.ses, to limit the length of the voyage by emptying the balloon 

 automatically. 



The instrumental equipment of baJlons sondes was first con- 

 sidered. M. Teisserenc de Bort presented a report on the 

 determination of height by the barometer. 



Drs. Assmann and Berson said that the usual methods gave 

 considerable errors, and they recommended the calculation of 

 the height by successive strata, applying a correction for the 

 change of temperature of the lower stratum during the ascent. 

 The Conference decided that — 



All nations should adopt the same formula of reduction, 

 whatever method might be chosen ultimately. 

 M. Teisserenc de Bort analysed the errors of the aneroid with 

 respect to the mercurial barometer, but in regard to the latter it 

 was pointed out by Dr. Berson that the mercurial column 

 only represents the atmospheric pressure at the moment when 

 the balloon has no vertical velocity. It was resolved that — 

 Simultaneous observations should be executed at the dif- 

 ferent stations, and that the instruments should be controlled 

 by taking them in manned balloons. Besides this, the instru- 

 ments ought to be interchanged among the different stations in 

 as short a time as possible. 



The determination of the temperature of the air in ballons 

 sondes was introduced by a report of M. Teisserenc de Bort. 

 Dr. Hergesell remarked that the temperature of the air varied 

 so rapidly that it was necessary to apply a correction-formula 

 which he had developed in the Meteorologische Zeitschrift, 

 December 1897. M- Cailletet exhibited a thermometer of his 

 invention, which had for its bulb a spiral silver tube soldered 

 to a glass tube, both being filled with the liquid toluene. 

 He stated that it acquired the surrounding temperature in 

 fifteen seconds. M. Teisserenc de Bort exhibited a self- 

 recording thermometer, having a thin blade of German silver 

 fixed in a frame of Guillaume's invariable steel. This instru- 

 ment takes the temperature of the air rapidly (9° F. in 

 fifteen seconds), and it is not affected by shocks. The ventila- 

 tion in a balloon is secured by a fan driven by a weight on a 

 wire, which falls 5000 feet in an hour and a half. Drs. Hergesell 

 and Assmann described their attempts to construct a sensitive 

 metallic thermometer, which the latter thought might be 

 ventilated by the agitation of the air through a jet of liquid 

 carbonic acid, but M. Cailletet pointed out that at low tem- 

 peratures the tension of carbonic acid is too slight to produce 

 ventilation. Dr. Berson remarked that in his high ascent, the 

 upper clouds, at an altitude of 24,000 to 29,000 feet, radiated 

 upon the instruments in the same way as does the surface of 

 the earth at a moderate height. As a result of the discussion 

 it was resolved — 



( I ) The rapidity of the thermometric variation is so great 

 in ballons sondes that to record it thermometers must be em- 



ployed which have much less thermal inertia than those 



hitherto employed, and (2) an efficient ventilation of the 



thermometers is indispensable. 



The testing of thermometers at temperatures below those to 

 which they would be exposed in ballons sondes was advised, 

 and Dr. Erk described the apparatus of Dr. Linde, of Munich, 

 for the production of a considerable quantity of liquid air. 

 This means of refrigeration enables temperatures lower than 

 200° C. below zero to be obtained. The Conference recom- 

 mended that — 



Before the ascensions of ballons sondes the instruments be 

 verified by varying the temperature and pressure under con- 

 ditions similar to those to which they would be subjected in 

 the atmosphere. 

 The equipment of manned balloons was next considered. 



Some remarks of Dr. Berson on the difficulty of reading a 



mercurial barometer, owing to the continual oscillations of the 



mercury, led to the following resolution : 



During ascents, the mercurial barometer is the standard 

 instrument for the comparison of aneroids, but for its observ- 

 ations to be trustworthy the acceleration must be zero ; it is 

 evident that this condition is fulfilled when the trajectory 

 traced by the self-recording aneroid is horizontal. 

 In consequence of the statement that it was possible to verify 



the instruments by reproducing the curves traced by them, the 



Conference advised that — 



There should be reproduced in the laboratory, with the aid 

 of pneumatic and refrigerating apparatus, similar curves to 

 those traced by the barometer and thermometer during balloon 

 ascents. 



Furthur discussion followed as to the methods of obtaining 

 the height of the balloon. M. Cailletet described his appa- 

 ratus for automatically photographing together, from lime to 

 time, the ground vertically below the balloon and the face of 

 an aneroid barometer. From a map the route of the balloon 

 as well as its true altitude are determined ; the pressure is de- 

 duced from the barometer, and thus the law connecting atmo- 

 spheric pressure with altitude can be studied. Photographs 

 have been taken from a balloon 7000 feet high, which was 

 moving forty to sixty miles an hour. The accuracy of these 

 measures was said to be within 1/250 of the height. It is pro- 

 posed to photograph a mercurial barometer in the same way. 

 The Conference recommended the use of M. Cailletet's apparatus 

 for both manned balloons and ballons sondes. The determination 

 of the height by observations at the ground was brought to the 

 attention of the Conference, and especially the " dromograph," 

 invented by MM. Hermite and Besanfon, for automatically 

 registering the azimuths and angular altitudes observed, and the 

 heliometer used by Dr. Kremser, of Berlin, for measuring the 

 apparent diameter of the balloon. 



Dr. Erk called attention to the fact that in the case of a large 

 difference of temperature between the wet and dry bulbs of the 

 aspiration psychrometer, the wet bulb always had in its im- 

 mediate neighbourhood a warmer body, which is the interior 

 cylinder surrounding it. The resulting error may be avoided by 

 covering the interior cylinder with muslin, so that the dry bulb 

 is protected by a cylinder having a temperature, t, and the wet 

 bulb by a cylinder having a temperature, /'. The Conference 

 thought it necessary that — 



The instrumental equipment of manned balloons should be 

 uniform, so far as possible. A recommendation has been 

 made in regard to the barometers ; concerning thermometers, 

 the opinion is expressed that the aspiration psychrometer 

 placed at the proper distance of at least 5 feet from the basket 

 is the only instrument which should be employed in manned 

 ascents. Simultaneous comparisons with the sling thermo- 

 meter are recommended. 



Drs. Berson and Hergesell urged the importance of simul- 

 taneous ascents in the different countries when a centre of 

 barometric depression existed over the European Continent. 

 From a purely meteorological point of view the manned ascents 

 have an importance which the ballons sondes do not, because 

 the temperature of these high regions can have no influence on 

 the meteorological elements near the surface of the earth. M. 

 de Fonvielle, however, insisted upon the interest of deducing 

 experimentally, from thermometric measures at a very great 

 elevation, the temperature of the supra-atmospheric medium. 



NO. 1503, VOL. 58] 



