SECTIONAL TRANSACTIONS.— A. 537 



closely with those obtained from the experimental work, assuming zero-point energy, 

 but deviate quite widely from those obtained without applying the correction for 

 zero-point energy. 



This appears to be a direct ' optical ' confirmation of the existence of such energy. 

 It is important to notice that the scattering power of an atom at large angles depends 

 almost entirely on the inner electrons, the effect of the outer ones being destroyed by 

 interference. The K electrons for an atom at rest are included within a domain whose 

 radius is considerably smaller than the amplitude of vibration due to the zero-point 

 energy. Thus the difference in the scattering curve for an atom at rest and for one 

 vibrating with this amplitude is considerable. 



Mr. DA^^D F. Martyn. — Frequency Variations of the Triode Oscillator. 



Previous theories of frequency variation are inadequate to account for the large 

 variations which can be obtained. A theory based on the flow of grid current is 

 outlined and shown to be capable of explaining all the observed variations in detail. 

 The conditions for the elimination of grid current are described, and it is shown that 

 when no grid current flows the frequency of the oscillator can be kept constant to 

 one part in 100,000 without special precautions, thus greatly increasing the value of 

 the triode oscillator as a means of making physical measurements of high accuracy. 



Afternoon. 

 Prof. E. Taylor Jones. — Lecture, with Demonatr&tion, on Spark Ignition. 



Department of Cosmical Physics. 

 Mr. A. H. R. GoLDiE. — Magnetic Storms : the disturbing Electrical Fields 

 as deduced from the records of the Magnetographs at Lerwick and 

 Eskdalemuir Observatories. 



The material used consists of magnetic records from the Meteorological Office 

 Observatories at Ler-«dck (Shetlands) and Eskdalemuir (Dumfriesshire), and in certain 

 cases also from Abinger (Surrey). 



Attention is first called to certain features of magnetic disturbance and of the 

 diurnal variation of magnetic force on disturbed days at the two Scottish observatories, 

 in relation to the corresponding changes at more southerly observatories. An attempt 

 is then made to compute the position and strength, hour by hour, of the electric current 

 sj'stem capable of producing the magnetic displacements recorded at the observatories 

 during certain magnetic storms of the year 1926. The features common to most of 

 the storms are found to be that during the afternoon and early evening period, and 

 again for some hours after midnight, the electric current system has at least approxi- 

 mately a linear resultant running roughly W.S.W. to E.N.E. The current in the later 

 of these two periods is oppositely directed to that in the earlier period, but the strength 

 and altitude are of the same order. In the later period also, in all cases examined, 

 the current position is farther north than in the earlier period, so that, though in 

 many cases the initial current lies between Lerwick and Eskdalemuir, no cases have 

 yet been found where the final current is not to northward of Lerwick. 



Mr. M. A. GiBLETT. — Wind Structure Research at the Royal Airship Works, 

 Cardington. 



The paper describes the experiments which are in progress at the Meteorological 

 Office, Royal Airship Works, Cardington, Beds, to determine the detailed structure 

 of the wind and the variations of the wind over short distances and in short intervals 

 of time. Four anemographs with specially open time scales and an electrically 

 controlled time-marking system are in use, the group of instruments being contained 

 in an equilateral triangle of side 700 ft. 



The various types of records obtained will be shown, together with some pre- 

 liminary results. 



An exhibit of records, &c., will be on view throughout the meeting as part of the 

 Meteorological Exhibition in the Randolph Hall. 



Mr. T. L. MacDonald. — The Probable Errors of Eye Estimations of 

 Planetary Detail. 



