SECTIONAL TRANSACTIONS. 



SECTION A. 

 MATHEMATICAL AND PHYSICAL SCIENCES. 



(For reference to the publication elsewhere of communications entered in the 

 following list of transactions, see p. 427.) 



CAPE TOWN. 



Tuesday, July 23. 



Prof. J. C. McLennan, F.R.S. — Some Recent Experiments on the Structure 

 of Matter at Low Temperatures. 



Prof. A. Fowler, F.R.S. — Standard Wave-Lengths in the Extreme Ultra- 

 violet. 



Measurements of spectra in the extreme ultra-violet can now be made with a 

 degree of accuracy approaching those of spectra in the ordinary regions, and the 

 establishment of standard wave-lengths has become a necessity. The paper gives 

 the results of a comparison of the wave-lengths of certain lines of aluminium and 

 silicon as determined by the coincidence method in different orders of the grating, 

 and by calculation from series relationships. 



Dr. J. S. VAN DER LiNGEN. — Spectroscopic Investigation of the Distribution 

 of Yttrium in certain Cape Granites. 



Sir Ernest Rutherford, O.M., Pres. R.S. — The Origin of Actinium. 



Dr. B. T. G. ScHONLAND. — Some New Electrometers. 



Geophysical Department. 



Joint Meeting with Section E {q.v.) for communications on Geodesy and 



Surveying. 



Wednesday, July 24. 



Presidential Address by the Rt. Hon. Lord Rayleigh, F.R.S., on 

 Some Problems of Cosmical Physics, solved and unsolved. (See p. 38.) 



Mr. R. H. Fowler, F.R.S. — Thermionic and other Emissions of Electrons 

 in the Light of Quantum Mechanics. 



The quantum theory allows us to calculate exactly the chance that an electron 

 will penetrate any sort of hill or pass by any rapid step of potential energy. Taking 

 any simple model of a metalUc conductor which conforms to the quantum theory, for 

 example, Sommerfeld's, which is Drude's modernised, we can calculate the rate of 

 emission of electrons from the conductor (1) when the conductor is hot; (2) when 

 it is cold, but subjected to a strong external field ; and (3) the efiect on the emissions 

 (1) and (2) of surface impurities represented by certain reasonable changes in the 



