3i6 



SECTIONAL TRANSACTIONS.— At . 



leads us to expect. Corresponding to very long Rayleigh-waves is an iL, 

 (about 4 km. /sec.) which travels with the velocity appropriate to Rayleigh- 

 waves in the ultrabasic material — i.e. about 4-4 X 0-92 km. /sec. These 

 two onsets, /Ll and zLr, are seen in the velocities found by the late Prof. 

 H. H. Turner for L ; sometinaes he found that for some earthquakes zL 

 fitted 0-42 min./deg., while for other shocks he found 0-47 min./deg. 

 These are evidently zLl and ?Lr respectively. 



The observations of group-velocity of Love-waves of known periods give, 

 on certain assumptions, an estimate of the thickness of the continental 

 granitic layer ; for Eurasia this is about 12 km., if it is assumed that there 

 is a tachylyte layer twice as thick as the granitic layer. 



For Rayleigh-waves in a surface layer the calculations are rather heavy. 

 The results available show that on the extremely hazardous assumption that 

 the floor of the Pacific Ocean is a layer of material of which the rigidity is 

 half that of the underlying material (this is roughly the case for tachylyte, 

 diorite, or syenite resting on dunite), the thickness of the layer is of the 

 order of 20 km. Further calculations are in progress. 



Mr. J. J. Shaw, C.B.E. — Earthquake recording in the heart of London. 



Dr. H. Jeffreys. — Near earthquakes. 



Mr. E. G. BiLHAM. — The climate of York and its variations during the 

 sixty years, iSyi-igjO. 



The paper is mainly devoted to a comparison of the climatological data 

 for York (the Yorkshire Museum) during the two periods of thirty years, 

 1871-1900 and 1901-30. It has commonly been asserted that since the 

 turn of the century winters have become less ' wintry ' and summers wetter 

 and less sunny. The data show that in the latter period mean temperature 

 has risen in most months, the increase amounting to from 1° to ij° F. 

 in January, March, May, October and December. Sunshine increased by 

 approximately 30 per cent, in November, and decreased by approximately 

 IS per cent, in February, March and May. Rainfall was on the average 

 7 per cent, less in the latter period, the months showing the biggest changes 

 being January (plus 12 per cent.), February (minus 15 per cent.), June 

 (minus 15 per cent.), July (minus 12 per cent.), September (minus 28 per 

 cent.), October (minus 17 per cent.), and December (plus 14 per cent.). 



The following table summarises the results for the four seasons and the 

 year, a positive sign indicating an increase in 1901-30 as compared with 

 1871-1900 (1S81-1900 in the case of sunshine) 



Season. 



Spring (March, April, May) 

 Summer (June, July, Aug.) 

 Autumn (Sept., Oct., Nov.) 

 Winter (Dec, Jan., Feb.) 

 Year .... 



The table supports the popular belief that winters have become milder, 

 but there is no support for the supposition that summers have, on the whole, 

 deteriorated since 1900. The season showing the most marked change is 

 autumn, with 17 per cent, less rainfall and 9 per cent, more sunshine. 



