641 TRANSACTIONS OF SECTION A. 



ascents. The usual inversions were experienced in the first three iilos. above the 

 earth'.i surface, after which the temperature fell steadily, in some cases the rate 

 exceeding by a slight amoimt for a kilometre or more the dry adiabatic. (See 

 C. 2 and D. 2.) In D. 2, C. 2, and P.H. 8 a very sharp rise of temperature is 

 noticeable just above the coldest point. 



Great differences are apparent in the temperature of the isothermal at 

 different places on July 27. C. 1 and L. 1 are in moderately close agreement at 

 about 230°, while P.H. 1 an4 C 1 show a temperature of below 220°. 



The difference between L. 1 and P.H. 1 amounts to practically 20°. 



On July 31 the i-ecords obtained at Manchester and Crinan are practically 

 identical for the isothermal. 



10. Observations of Currents in the Upper Air of Eyypt and the Sudan. 

 By Captain H. G. Lyons, F.B.8. 



11. An Aj^paratus for ilhtstrating, by Intermittent Vision, the Surface 

 Movement of Air in Travelling Storms. By R. G. K. Lempfkrt, M.A. 



This apparatus, by the use of which intermittent vision of a succession of 

 maps is obtained through parallel slits in a revolving drum, has been arranged at 

 the Meteorological Office to visualise simultaneously the trend of a ' storm ' across 

 the map and the surface movement of air within the storm area. 



The consecutive maps have been drawn for intervals of one, or at most two 

 liours. "\^^hen placed in position, they form an inner lining to a drum, with slits 

 in its upper part, attached to a revolving hori::ontal, after the manner of the toy 

 linowji as a 'zoetrope.' The position of the sorm ' is represented on successive 

 maps by the isobars which show the barometer distribution. The movement 

 of the air within the storm area is shown by ai rows, each one of which represents 

 a 'step' in the motion of the air. As the drum is revolved, the isobaric systems 

 appeal' to travel across the map and the arrows to move forward, tracing out the 

 ' trajectories ' or paths of the air. 



12. Oil the Asymmetrical Character qf Whirhvinds. By Paul Dukandin. 



WEDNESDAY, SEPTEMBER 0. 

 The following Papers were read: — 



1. Changes of Atmospheric Density in Storms. By J. I. Craig, M.A. 



A -iuass of air whicb expands without gr iniug heat necessarily experiences 

 cooling, and this mechanical cooling is now generally admitted by meteorologists 

 to be the chief cause of rain. Such an expansion occurs when air is transported 

 from a lower to a higher level. The paper shoved that a similar expansion takes 

 place in front of the trough of depressions of both the cyclonic and the V-shape, 

 and that there is a certain amount of correspond snce between the region of greatest 

 surfacs dilatation and that of heaviest rainfall. In rear of the trough the dilation 

 is negative, on the whole, but with isolated positive regions — a fact which may 

 help to account for the ' passing showers ' generally found in rear of baric 

 depressions. 



' T/w Life Uisionj of Surface Air Curn-nts. Louduu : H.M, Statiuneiy Office, 

 J.906. 



