364 SECTIONAL TRANSACTIONS.—A. 
CosmicaL PHysics SUB-SECTION. 
19. Mr. F. J. W. Wutrertr.—The Diurnal Variation of Pressure: 
Facts and Theories. 
The regular oscillation of pressure shows remarkable regularities all over 
the globe, and it is, therefore, probable that it is connected in a simple way 
with its cause. The object of this paper is to emphasise the fact that there is 
an opening here for speculation as well as for more analysis of the records. 
The preparation of critical tables of pressure at places where barographs have 
been maintained for long periods requires international co-operation. Observa- 
tional material is exceptionally rich in the British Isles, where a number of 
photographic barographs properly compensated for temperature changes and 
with open time-scales have been in operation for more than fifty years. The 
British records indicate that the average diurnal variation of pressure for a 
given time of year can be regarded as due to the combination of a local wave’ 
(a pure sine-curve) and a planetary wave. The planetary wave is not a pure 
sine curve; the changes in its form conform closely to changes in the sun’s 
declination. It is pointed out that these facts are difficult to reconcile with 
Lord Kelvin’s resonance hypothesis, and in conclusion other objections to that 
hypothesis are also mentioned. 
20. Prof. W. J. Humpureys.—The Relation of Wind to Height. 
On the average, perhaps, and especially on the equatorial side of cyclones, 
the wind varies as follows with height : Increases rapidly, but decreasingly so, 
with height up to 400 to 500 metres above the surface; then decreases slightly 
through, say, 300 metres ; after this increases a little, and then remains, roughly, 
constant up to round 2,000 to 3,000 metres above the surface; here again often 
slightly decreases; and then through the next several kilometres increases in 
proportion to decrease of density. Directions of the wind and its temperature 
also are interestingly related to height above the surface. 
All these observed facts are plausibly explained as effects of mechanical 
and thermal turbulence. 
21. Mr. J. Bserxnes.—The Importance of Atmospheric Discon- 
tinuities for Practical and Theoretical Weather Forecasting. 
Empiric investigations show that new-formed depressions usually consist of 
two oppositely directed air currents, the one warm and the other cold. Initially 
each current occupies about one-half of the region covered by the depression. 
The area of the cold air is, however, always increasing, and finally it embraces 
the whole of the depression in the lower layers. The warm air covers at the 
ground a correspondingly decreasing space (the warm sector). During the 
development of the depression, air from the warm sector will escape upwards 
‘and spread in higher layers. This motion involves a transformation from 
potential into kinetic energy (strengthening of the wind and deepening of the 
depression). The kinetic energy of the depression decreases again as soon as 
there is merely cold air supply available for the ascending motion. The tem- 
perature distribution in the depression thus gives useful indications concerning 
the expected development. 
The result may be formulated mathematically as an equation giving the 
acceleration of the different air masses relatively to each other. One may thus, 
at least theoretically, arrive at a mathematical forecast, provided that sufficient 
observational data are at hand. This is exemplified in a depression passing 
Central Europe on February 1, 1923. 
22, Mr. L. F. Ricuarpson.—Turbulence and Temperature-gradient 
among Trees. 
The writer has previously derived from theory a criterion for the increase 
of turbulence, applicable at a height in the free air great compared with the 
irregularities of the ground. By contrast: the present investigation relates to 
PR ai > be, 
