143 
1916-17.] The Formation of Anticy clonic Stratus. 
commoner than the type which would be obtained from the curve on the 
left-hand side by adding to the temperature an amount which increased 
continuously witlrthe height. The figure illustrates how reversed gradients 
may be produced in this way from the inequalities in the temperature 
gradient which may always be expected to exist. 
Layers of stratus appear often to be produced in this way when there 
is a rising temperature, especially in winter ; near the northern boundary 
of the anticyclone there may be more than one layer, at different heights. 
During the spring and summer of 1916 good instances of stratus formed 
in this way occurred in Northern France on March 31, May 17, and 
June 21, with a west wind, and on July 21 with a north wind, which 
had spread round from the west ; the figures for some of these instances 
were given in my earlier paper. 
On the southern and western sides of anticyclones in Northern France 
in summer, solar radiation affected the temperatures to such an extent 
that no definite conclusions could be reached. There was occasionally an 
adiabatic gradient up to 10,000 feet. During the winter, in Northern 
France and Britain, stratus is common with easterly winds. In some 
cases this may have formed originally with a west wind, but probably it 
is more often formed as the result of cold air flowing under warm air. 
Mr Cave shows that very often the east wind increases to its gradient 
velocity at the height of about a kilometre, and then decreases. Probably 
the layer of maximum wind velocity is a layer of minimum temperature, 
and usually contains haze and some cloud.* 
On the eastern sides of anticyclones cold air from the Arctic Sea some- 
times flows under warm air. An instance of this occurred on June 15th- 
18th, 1916; on the 16th at 2 p.m. the temperature was 58° F. at the 
surface, 40° at 3500 feet, 43° at 4000 feet, 38° at 7500 feet, with haze up 
to 3500 feet and some stratus patches from 3000 to 3500 feet. On that 
occasion the wind did not decrease in velocity above the clouds, but there 
appeared to be an increase of the W. to E. component ; this was probably 
due mainly to the horizontal temperature distribution, but perhaps partly 
also to the fact that the air constantly required to reinforce a northerly 
current was flowing from the west across the anticyclones, as suggested 
by Sir Napier Shaw in “Principia Atmospherica.” The cirrus motion on 
the day in question was from the west. If the stratus clouds represented 
the dividing layer between two bodies of air of widely different origin, 
* Probably the turbulence of the lower layers is of importance in these cases ; other- 
wise there would probably be an adiabatic gradient up to the level of greatest wind velocity, 
and above that a constant low gradient. See Note at end. 
