TBANSACriONS OF SECTION A. 593 



(i) l%eodotite Obaervations of JJalloom penelraliny the Isothei'inal Lni/ei'. 



By C. J. P. Cave. 



At the end of July, on the days arranged for balloon ascents by the Commis-" 

 sion for Scientific Aeronautics, theodolite observations were made at Ditcham 

 Park on four ballons-sondes carrying instruments, and on one large balloon of the 

 same kind, but carrying no instrument. The balloons used were supplied by 

 M. Paturel of Paris, and were nominally 1'75 metre in diameter; their weight 

 was about 02 kg., and they were filled with hydrogen to lift 0-8 kg. in addition 

 to their own weight ; the instrument, label, and string weighed from 75 to 80 

 grammes; there was also a balloon nominally of 1 metre in diameter and weio-h- 

 ing 80 grammes, filled to lift 30 grammes in addition to its own weight ; it 

 trailed below the instruments during the ascent, and was intended to serve as a 

 check to the descent and as an aid to the finding of the instruments.' The large 

 balloons were uncoloured, and were very plainly visible by reflected sunlight 

 against the clear sky. The ascents began about an hour before sunset. 



Observations were made by means of two theodolites placed about 2-68 km. 

 apart; owing to the distance to which the balloons went, and sometimes to their 

 direction with regard to the base-line, it was not possible to plot the more 

 distant part of the trajectories from the two sets of observations; accordinglv 

 the rate of ascent was determined up to the point at which the two-theodoliti^ 

 method ceased to be reliable, and was subsequently assumed to be uniform, and 

 the positions of the balloon were plotted from the observations of one theodolite. 

 It is probable that the balloons did not ascend with uniform velocity ; the velo- 

 city probably increases as the balloon ascends. The assumption of a uniform velo- 

 city, however, probably gives a fair approximation of the trajectories of the 

 balloons. From the plotted trajectories the wind velocities are determined for 

 each minute interval, and are finally plotted to show the relation of wind velocity 

 to height. 



The first balloon of the series was sent up on July 27, but was lost to sight 

 at a height of about 8-5 km. The balloon of July 28 was kept in sio-ht to a 

 height of 13 km. ; the wind velocity increased from about 5 miles an hour at 

 2 km. to 50 miles per hour at 8 km. ; above this it remained fairly constant to 

 11 km., when there was some increase, a maximum between 50 and 60 miles per 

 hour being indicated at 11-5 km. ; above this the velocity decreased ra'pidly, 

 being about 8 miles per hour at 13 km. ; the wind, which had been from the north 

 or a little west of north, was more from the west at the greatest heights. The 

 record from the meteorograph carried by this balloon shows that the isothermal 

 layer was entered at 11"5 km. The wind velocities for July 29 are verv 

 similar to those for the previous day, the maximum of from 50 to 60 miles per 

 hour being reached at 11-5 km.; the subsequent decrease, however, was not so 

 rapid, the velocity being still 20 miles per hour at 13-2 km. The balloon of 

 July 30 shows smaller wind velocities above 7 km. than on the three previous 

 days, the wind being fairly steady at from 25 to 30 miles per hour; there was 

 some increase at 10"5 km. to 35 miles per hour, followed by a slow but steady 

 decrease to 25 miles per hour at 11-7, when the balloon was lost to sight. Un- 

 fortunately the balloons of this and the previous day went out to sea and the 

 meteorographs were not recovered. On July 31 a 1-75-metre balloon filled to 

 the same amount as the balloons of the previous days, was sent up without 

 instruments : this showed very large wind velocities, increasing from 10 miles per 

 hour at ground level to 80 miles per hour at 11-5 km. ; above this there was a de- 

 crease to about 55 miles per hour at 13-5 km., when the balloon was seen to burst. 



In all cases, therefore, in which the balloon was watched to heights of above 

 11 kilometres the wind velocity reached a maximum value at a little above this 

 height, followed by a decrease above. 



' Owing to the small balloon the instrument of July 2S was recoverej • it fe'l 

 in the Channel, and the balloon kept it afloat for three days. ' 



1%8. . - QQ 



