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SCIENCE 



N. S. Vol. XXX. No. 763 



besides the ground observations, only pilot- 

 balloons need be sent up, but sufficient in 

 number to serve as a basis for charts of 

 air movements. 



Professor Bjerknes endorsed Professor 

 Koppen's proposition to use dynamical 

 units to express atmospheric pressure and 

 wind-velocity, and in replying to questions 

 as to the advantage of absolute measures 

 he said that they avoided the introduction 

 of constants in the application of dynamic 

 equations and thus gave precision and sim- 

 plicity. Tables facilitate the transforma- 

 tion of the old into the new units. Mr. 

 Cave, of England, said that the upper-air 

 observations in England were now pub- 

 lished in the Weekly Weather Report in 

 absolute units. 



Mr. Cave read a request from his col- 

 league, Mr. Dines, to have the hallons- 

 sondes sent up about an hour before sun- 

 set to avoid insolation and yet allow them 

 to be watched with a theodolite. Professor 

 Eotch said that this practise had given 

 good results in America, but the conference 

 was unwilling to change the existing hour. 

 It was later voted that beginning in July, 

 complete observations be obtained as nearly 

 as possible at 7 a.m., Greenwich time, as 

 heretofore, but that pilot-balloons be sent 

 up three times a day as desired by Pro- 

 fessor Bjerknes during one of the monthly 

 series of ascensions. There was also voted 

 in this connection, a proposition of M. Vin- 

 cent, to observe the state of the sky on the 

 international days. 



M. Teisserene de Bort, of Paris, spoke on 

 the result of his triangulation of ballons- 

 sondes from 1898 to 1909 at Trappes and 

 their importance for the verification of 

 heights calculated by the barometer. The 

 base-line used was 1,300 meters, but there 

 is now a base of 5,000 meters. While the 

 two methods agreed closely, the effect of 

 hysteresis in the barometer was evident, 



though the temperature-correction was 

 small. M. Teisserene de Bort exhibited 

 charts of some trajectories of his balloons, 

 which showed that the cyclonic rotation 

 ceases at a certain height and is replaced 

 by a calm zone that marks the top of the 

 adiabatic temperature-gradient. Above 

 this the currents are from the south and 

 west and opposed to the surface-wind. In 

 the tropics, superposed currents occur with 

 a sudden change in direction at about 7,000 

 meters, the absence of cyclonic storms ac- 

 counting for the stratification. As to the 

 changes of wind in the "stratosphere," or 

 region of the upper temperature-inversion, 

 M. Teisserene de Bort had found only 

 slight changes, but Messrs. Cave and Her- 

 gesell agreed that the velocity of the wind 

 decreased there. Professor Hildebrands- 

 son 's observations of clouds confirmed those 

 of M. Teisserene de Bort with balloons, in 

 showing a motion towards the north above 

 3,000 meters over a low-pressure area. 



Continuing the technical questions, Pro- 

 fessor Hergesell discussed the upward ve- 

 locity of rubber balloons as a function of 

 their lift and the use of pilot-balloons to 

 determine the vertical currents of the at- 

 mosphere. In a closed space the velocity 

 remains constant, so that, knowing the sur- 

 face and free-lift of a balloon, its rate of 

 ascent may be calculated, and there is little 

 difference— about 4 per cent. — between the 

 height obtained from angular observations 

 of the balloon at one station, combined with 

 its assumed velocity, and measurements of 

 its height from the ends of a base-line. 

 Successive observations of the displacement 

 of the balloon enable the speed of the hori- 

 zontal wind to be determined accurately. 

 Often the vertical currents may be meas- 

 ured from angular observations at the cor- 

 ners of a triangular base, and a downward 

 movement of 1.5 meters per second has 

 been measured. In the discussion Captain 



