————— 
———— 
SECTIONAL 'TRANSACTIONS.—A. 411 
The curve to be investigated is made into a template and pushed under the 
strings at a point corresponding to the interval which it is desired to test as 
being the suspected length of the period. ‘The resulting movement of all the 
strings is averaged out into the movement of the spot of light from the optical 
lever. Both the length and amplitude of the period may thus be determined 
with fair accuracy. The outstanding advantage of the device is its simple 
construction and the rapidity with which it may be used, once the template has 
been prepared. , 
14, Dr. Dawson Turner and Mr. D. M. R. CromBIE.—Demonstration 
of the Behaviour of an Electrified Pith Ball in an Ionised 
Atmosphere. 
The experiments included those showing the effectiveness of various sources 
of ionisation, such as an are light, burning magnesium wire, incandescent 
platinum wire, Nernst filament, a Bunsen flame, X rays, and radium rays. The 
directive influence of the charged Leyden jar was demonstrated by the concentra- 
tion of the ions along a line joining the centre rod of the jar and the source of 
ionisation ; for unless the pith ball be in this line it appears to be unaffected. 
A comparison between the sensitiveness of the charged pith ball and an electro- 
scope as indicators of the presence of an ionised atmosphere was attempted. The 
ions tend to be carried upwards by convection currents. ‘lhe effect upon the 
pith ball appears to be independent of the nature of its charge. 
During the afternoon, also, an exhibition of physical apparatus of 
historical interest, arranged by Dr. Carse, was on view. In addition, 
Prof, Whittaker invited members of the Section to see the Mathematical 
Laboratory. 
Friday, September 9. 
15. Presidential Address by Prof. O. W. Ricuarpson, F.R.S., on 
Problems of Physics. See p. 20. 
16. Joint Discussion with Section B on The Structure of Molecules. 
See p. 468. 
In the afternoon a visit to the Royal Observatory took place. 
Monday, September 12. 
17. Discussion on The Quantum Theory. See p. 473. 
(2) Department oF CosmicaL Puysics. 
18. Mr. Carte Satter.—The Drought in England during the Summer 
1921. 
19. Mr. W. H. Dives, F.R.S.—The Discontinuity of Temperature at 
the top of the Troposphere. 
90. Prof. A. Kritorr.—The Magnetic Anomaly in the District of 
Kursk. 
(b) DepaRTMENT oF Puysics. 
21. Prof. C. G. Barxua, F.R.S.—The Energy of X Radiation. 
22. Dr. Hans Perrersson.—Internal Movements in the Sea. 
The stratification of the sea-water, consisting in a superposition of water- 
layers different in salinity, temperature, and density, different also in biological 
respects, is a normal condition always to be found where large masses of 
fresh or brackish water are being carried out to sea. The Baltic, the Kattegat, 
and the Skagerak are typical examples, and so, according to the results of 
Johan Hijort, is the Gulf of St. Lawrence and the Newfoundland waters. 
FF2 
