356 SECTIONAL TRANSACTIONS,—A.1T 
been confirmed in the laboratory, and that if an attempt is made to calibrate Rowland’s 
scale of intensities, using Unsdld’s formula, the result does not agree with Adams and 
Russell’s calibration, based on multiplet intensities. A direct check on Unsdld’s 
formula is provided by telluric oxygen lines. These increase in width as the sun 
sinks from the zenith, and from them the relation between line width and number of 
absorbing atoms can be found. The experimental result shows a distinct deviation 
from Unsdld’s formula. 
On the theoretical side the phenomenon of interlocking has been neglected, that 
is to say, the necessary connection between lines having the same upper state has 
an effect on the intensities of these lines in absorption, which is not taken into account 
by the elementary theory. Further, it is assumed that when an atom absorbs a 
quantum in the wings of a line, it must necessarily emit a quantum of exactly the 
same frequency, and not, for example, sometimes emit the central frequency of the 
line. Nolaboratory evidence on this point is available. The astrophysical phenomena 
may throw light on this and on other questions connected with resonance radiation, 
which have so far proved too difficult to observe in the laboratory. 
Dr. B. F. J. ScHontanp.—Lvghining. 
An account will be given of recent investigations upon thunderstorms in South 
Africa, and their bearing upon the question of lightning discharges between the cloud 
and the ground. Evidence will be presented which makes it difficult to accept the 
view that the branches in a lightning flash fork away from the positive pole of the 
discharge. 
Mr. R. A. Watson Wart and Mr. O. F. Brown.—Radio Research in the 
British Empire. 
While the participation of the British Government in radio research dates back 
to the experiments of Captain Jackson in the Navy and to the contemporaneous 
co-operation of the Post Office in Mr. Marconi’s early work, it was not until the 
formation in 1921 of the Radio Research Board, under the Department of Scientific 
and Industrial Research, that a systematic programme of fundamental research was 
undertaken under official auspices. The present communication deals chiefly with 
the results obtained in the research work carried out by the Board, which has been 
_ concerned very largely with the effects of the media on the propagation of electro- 
magnetic waves and with the nature and origin of atmospherics. It then refers to 
the corresponding Dominion institutions more recently established in Australia, 
New Zealand and Canada, and to the problems which they are attacking. Special 
reference is made to the necessarily world-wide scope of fundamental radio research. 
Monday, September 28. 
Discussion on Magnetic Storms and Ionisation in the Upper Atmosphere. 
(Prof.8. Coapman, F.R.S.; Prof. E. V. APPLETON, F.R.S.; Mr. A. H.R. 
GotpiE; Mr. W. M. H. Greaves; Prof. J. C. McLennan, F.R.S.) 
Prof. EK. V. AppLeton, F.R.S. 
The evidence of wireless transmission has shown that there are two principal 
regions in the upper atmosphere responsible for the reflection of wireless waves. The 
diurnal and seasonal variation of the ionisation in the lower one (the Kennelly-Heavi- 
side Layer) has been studied in some detail during the past year. The maximum 
noon ionisation is found to be six or seven times that at midnight, while summer 
noon ionisation is two and a half times that at winter noon. The corresponding 
relations for the upper region, the ionisation content of which is greater, have not 
yet been determined in such detail, but it is believed that the diurnal and seasonal 
variations are not so large. 
Observations made during periods of magnetic activity show that the principal 
change from normality is in the lower region, where the ionisation is usually increased. 
A common occurrence is for the ionisation to be increased two or three times. 
The theory of Maris and Hulbert (based on the experiments of Hafstead and Tuve) 
