642 TRANSACTIONS OF SECTION A. 



8. Note on the Manchester ' Bcdlons-Sondes ' Ascents. 

 By W. A. Harvvood. 



In connection witli the Howard Estate Observatory of the Manchester Uni- 

 versity, ballons'sondes ascents have been made regularly during the past year on 

 the dates appointed by the International Committee. 



The balloons are of tine sheet rubber, and carry light instruments of the type 

 devised by Dines. These record pressure and temperature. The total weight of 

 instrument and case being only two ounces allows the use of relatively small and 

 inexpensive balloons. 



The majority of the ascents have been made after sunset, to avoid possible 

 errors due to solar radiation ; but the similarity of the results obtained by day and 

 night tends to show that the instrument is sufficiently ventilated to prevent 

 serious errors being introduced from this cause. 



The instrument was carefully calibrated before and after each ascent, the rela- 

 tion between deflection and pressure being determined for a number of diiferent 

 temperatures. 



The results have been of fairly uniform type. 



In general the temperature falls steadily at a slightly increasing rate up to 

 a height of about 10 kms. The gradient then quickly diminishes to zero, or to a 

 small positive or negative value. 



The average height at which the isothermal layer was encountered is about 

 11'5 kms. This height is slightly greater (12 kms.) above auti-cyclones, and 

 slightly less (1 1 kms.) above cyclones, as has been previously found. 



The lowest temperature which has been recorded is — 65° 0. on February 6, 

 1908, at a height of 11 kms. 



The conclusion that the lowest temperatures are found above anti-cyclones 

 has been verified, the average minimum temperature being —55° C. compared 

 with corresponding cyclonic temperature - 46° C. 



On an average three-fourths of the instruments have been returned. 



The usual practice has been to give the balloons a free lift, about 70 per cent 

 of the total weight. This gives the greatest heights combined with the greatest 

 percentage of balloons returned. 



As might be expected the percentage of instruments found is greatest in 

 anti-cyclonic weather. The average distance traversed by the balloons is about 

 sixty miles, and the mean direction E. by S. Consequently the most favourable 

 starting-point would be in the neighbourhood of Shrewsbury. 



9. T}i,e Results of the ' Ballons- Sondes ' Ascents in the British Isles during 

 the International Week, July 11-Atigust 1, 1908, By 3. S. DiNES. 



The places of fall of the instruments were plotted on a map and exhibited 

 as a lantern slide. Of the five stations from which ascents took place, it may be 

 mentioned that Crinau is on the West Coast of Scotland, Pyrton Hill about fifteen 

 miles south-east of Oxford, and Ditcham Park a little to the north of Portsmouth. 

 It is generally found that the tracks of the several balloons sent up from the 

 different stations on the same day are approximately parallel, and this was the 

 case on the days of the international week, with the exception of July 29, On 

 this day a high-pressure system was situated with its centre over the south-western 

 part of the British Isles, and the direction of travel of the different balloons seems 

 to have agreed closely with the circulation around this centre. On the other 

 days of the week the high-pressure system was more remote. 



The subjoined diagram shows the relation between the temperature (on the 

 absolute scale) and height above sea-level (in kilometres). The numbers against 

 the curves refer to the days, so that all ascents on tne same day have the same 

 number. The different stations are denoted by the letters. All the ascents were 

 made near the time of sunset except C. 6. The temperature near the highest 

 point in this case showed rather a sharp rise, and as this may have been due to the 



