SECTIONAL TRANSACTIONS.— A, Af. 315 



Different critical dimensions are necessary when frames are used for 

 transmission. 



The word ' formatised,' as distinct from ' tuned,' is suggested for such 

 critically proportioned frames. 



Prof. D . A . Keys. — Magnetic and electrical surveys over mineral, diabase and 



artificial dikes. 



Magnetic dikes which do not outcrop may be located and their strike 

 and dip determined with fair accuracy with the modern types of horizontal 

 and vertical magnetic variometers. As a result of calculations and labora- 

 tory experiments, magnetic measurements may also be used to determine 

 approximately the amount of overburden and to estimate the vertical height 

 of the dike. Resistivity and electromagnetic geophysical methods may be 

 applied to confirm these results and to distinguish mineral from diabase 

 dikes. 



Examples of the variation in horizontal and vertical intensities over 

 magnetic models were given. The results of surveys made over buried 

 diabase and pyrrhotite nickel dikes in the Sudbury Basin, Ontario, indicate 

 the possibilities of these magnetic and electrical methods. The geophysical 

 interpretation of the results over the pyrrhotite vein indicated the proper 

 strike and dip of the dike and the amount of overburden, as was determined 

 from diamond drill records. The electrical methods differentiated the 

 diabase from the pyrrhotite dike. 



The strike of these dikes was approximately east-west, but the methods 

 may also be extended to buried veins lying in other directions. This 

 investigation was carried out in collaboration with Prof. A. S. Eve, F.R.S., 

 and Dr. F. W. Lee. 



Prof. G. Temple. — Certain aspects of Quantum Theory. 



DEPARTMENT OF COSMICAL PHYSICS (Af). 



Thursday, September 1 . 



Dr. R. Stoneley. — The long-wave phase of earthquake records. 



The long-wave phase, the beginning and the maximum amplitude of 

 which are respectively designated as L, M on seismograph records, consists 

 mainly of waves that have travelled over the surface of the earth. These 

 waves are of two types — the Rayleigh-waves, in which there is no displace- 

 ment perpendicular to the plane through the vertical and the direction of 

 propagation, and the Love-waves, in which the displacement is in this 

 direction only. Accordingly, the waves are best- studied in records of 

 shocks that arrive in a nearly due easterly or westerly azimuth : the N.-S. 

 record then shows the Love-wave and the Rayleigh-waves are recorded on 

 the E.-W. and Z records. 



Both types of wave show dispersion — i.e. dependence of velocity on 

 period — and the velocity of travel of a given group of waves is the ' group- 

 velocity.' The various maxima observed presumably denote the arrival of 

 waves of stationary group-velocity. The ?L corresponding to the sudden 

 commencement of the surface waves, corresponds to Love-waves of very 

 long period, and the velocity of about 4-4 km. /sec. is that of distortional 

 waves in the ultrabasic substratum below the surface layers, as general theory 



