140 Proceedings of the Royal Society of Edinburgh. [Sess. 
Thus a general increase of temperature took place except at about 
10,000 feet, but the effect of convection from the ground within the lower 
adiabatic region was probably considerable. The wind was very light from 
the N.E. on the 25th and from the E. on the 26th, Northern France being 
under the influence of a shoulder of a large anticyclone centred over Russia. 
During the period July 29 to August 1, 1916, there appeared to be 
general warming due to descent, but the effect of convection with the 
surface layer maintained the level of the top of the haze at about 4000 
to 5000 feet; it reached the former height in the mornings, the latter in the 
evenings. The wind was very light from the N. or N.E. throughout the 
period. 
In Scotland, when anticyclonic ridges arrive from the west I have often 
observed an effect apparently due to descent ; the clouds which are usually 
present on the north-eastern sides of anticyclones dissolve away when the 
wind falls to a calm or light air. 
Sir Napier Shaw * has shown that a current from south to north 
constantly tends to thicken, and can only be steadily maintained if there is 
an outflow for the excess air ; this usually takes place close to the surface 
towards the west, and helps to explain the descent which appeared to 
take place behind the anticyclone of September 22-25 already referred to. 
In the same paper it is suggested that when a southerly current lies to the 
west of a northerly current, part of the excess air of the former may cross 
the high-pressure area and supply the reinforcement which is constantly 
required by the latter. If this takes place it would greatly help to explain 
the vertical temperature distribution of the northerly currents of anti- 
cyclones. 
Suggested Explanations of Reversed Gradient. 
In considering the origin of anticyclonic stratus and the accompanying 
vertical distribution of temperature, the difficulty lies not so much in 
accounting for the relatively high temperatures found at high levels, as in 
explaining the discontinuity involved in the well-marked reversed gradients. 
We will first consider the effect of increasing pressure on cloudy air. 
The increase of pressure will raise the temperature except where clouds are 
present ; the amount of cloud will be diminished, but those regions where 
there was originally most cloud will become regions of minimum tempera- 
ture, with or without cloud. It is true that stratus could be formed in this 
way only if there was already some degree of stratification in the 
* “ Principia Atmospherica : a Study of the Circulation of the Atmosphere,” Proc. Roy. 
Soc. Edin ., vol. xxxiv, 1914, pp. 77-112. 
