SECTIONAL TRANSACTIONS.—A*, Af. 351 
The idea which has enabled an analysis to be completed of the arrangement of the 
different solutions through a single starting-point (0, x) was described in more detail. 
The idea consists in using the one-parameter family of special solutions known as 
Emden’s Solutions as a grid or co-ordinate system to which the behaviour of the 
other solutions can be referred and thereby disentangled. It is first necessary to 
determine when the Emden’s Solutions are so arranged themselves that they have 
suitable properties for a co-ordinate system. The method proves successful here, 
but the complete results can be obtained in other ways and it does not seem likely 
that the new method will prove of much wider utility. 
——-”- 
DEPARTMENT OF COSMICAL PHYSICS (Af). 
Thursday, September 24. 
Dr. J. Bsexxnes.—Tropopause Waves. 
The lowest part of the atmosphere—the troposphere—is characterised by a 
general decrease of temperature from the ground upwards with a lapse rate of about 
O°6 C. per 100 m. The overlying part of the atmosphere—the stratosphere—is 
over the temperate zone usually characterised by an almost constant temperature and 
over the intertropical belt by an increasing temperature with height. The surface 
of separation between troposphere and stratosphere, the so-called tropopause, is on 
an average at 17 km. level over the equatorial belt and descends from there polewards. 
Over the North Pole the height of the tropopause is probably about 8-9 km.; over 
the South Pole its height is unknown but certainly still lower than over the North 
Pole. Over the temperate zone at about 50° N., from which most of the upper air 
observations are gathered, the tropopause slopes downwards towards the pole with 
an average inclination of 1 in 800. 
‘ Whenever the weather situation at the ground is changing, the tropopause is 
_ lowered beneath or raised above its average level. These changes of level of the 
_ tropopause may usually be ascribed to the passage from west to east of a series of 
wave-like disturbances which are here referred to as tropopause waves. The 
structure of the tropopause waves is shown by aid of vertical and horizontal cross- 
sections based on observational data. It is being shown that the orbital plane of 
the tropopause waves is almost horizontal, and that the change of level of the tropo- 
_ pause is, therefore, not due to a vertical displacement, but to a horizontal displacement 
of the air polewards or equatorwards. The cause of the tropopause waves is sought 
in the action of the polar front disturbances in the lower troposphere on the air 
currents of the upper troposphere. The importance of the tropopause waves for 
certain weather phenomena is discussed. 
Sir Girpert WALKER, F.R.S.—Stratified Clouds. 
It was shown by E. H. Weber in 1855 that in the absence of shear, polygonal 
‘patterns were set up in a vertically unstable layer of liquid and in 1920 by Idrac 
that a rapid shear produced longitudinal vortices. In 1929, S. Mal, at the Imperial 
College, obtained rectangular cells with slow shears; he also verified by observations 
in Berlin that (a) when strata of clouds break up they are vertically unstable, and (6) 
the rate of shear is minute, rapid or slow according as the cloud pattern belongs to 
first, second or third type above indicated. This year A. C. Phillips and I have 
erimented with air drawn through a small wind channel, the motion being made 
ible by fumes of titanium tetrachloride; with rapid shear, instability caused 
gitudinal vortices with less rapid rather complex cross patterns ; with slow shear, 
fransverse vortices, and with no shear polygons whose sides were vortices. 
__ In Mal’s work the liquid always{ascended in the interior of a cell and descended in 
the interlaces between cells; but in our experiments with air the descent was inside 
the cells. In actual clouds there is usually ascent within the polygons, but descent 
is by no means rare. 
