462 SECTIONAL TRANSACTIONS .—Af. 
to the Ordnance Survey geological map of the area shows that this position 
lies on a fault which runs for about two miles in a north-easterly direction 
from the head of the Dale. 
From this epicentre distances were calculated to all the observatories—11 
in number—from which records were available, and a time-distance diagram 
was plotted for all the points measured on the seismograms. From this the 
travel-times, velocities and apparent delays in starting of the six phases 
exhibited in the following table were deduced. 'The values obtained by 
Dr. Harold Jeffreys for two previous British earthquakes are given for 
comparison. 
WENSLEYDALE. JEFFREYS. 
Vel. Delay. Vel. Delay. 
Phase. km./sec. sec. km./sec. sec. 
P 8°55 II 7°8 9 
Pp* 6°21 2 6°3 5 
Pg 5°23 6 574 3 
S 4°29 10 4°35 8 
S* 3°54 ° Shh 4 
Sg 3°30 4 3°3 ° 
It will be noted that whilst the velocity of the Sg wave is identical with 
that previously found, that of the P wave is appreciably higher, and all the 
rest are slightly lower than the normal. The apparent times of starting also 
follow a different order. ‘These anomalies may be related to depth of focus, 
which appears to have been somewhat greater than normal. In determining 
the epicentre from the three nearest stations, it was found impossible to 
obtain intersecting circles by adopting the velocities appropriate to Pg and 
Sg, but good concordance was obtained by taking those of P* and S*. 
It should be stated that at all the stations except Stonyhurst and Durham 
the movements recorded were extremely small, rendering measurement and 
identification of phase difficult, so that any conclusions arrived at can only 
be taken with some reserve. ‘The points measured, however, lie very well 
on the straight lines corresponding to the values in the above table, which 
accordingly seems to be fairly well established. 
Mr. A. C. Best.—Temperature gradients near the ground (11.0). 
A paper was read at the British Association Meeting in 1925 by N. K. 
Johnson, describing the results obtained from a study of the vertical gradient 
of temperature in the atmosphere over the height interval 1-2 m. to 17°1 m. 
These results were subsequently amplified and published as a Geophysical 
Memoir by the Meteorological Office. 
The apparatus used by Johnson has remained in use since that date, and 
in 1931 additional apparatus was erected by the author with a view to 
examining the temperature gradient below 1-2 m. 
Records of the temperature differences over the height intervals 2-5 cm. 
to 30 cm. and 30 cm. to 120 cm. over close cropped grass have been 
obtained for approximately two years by means of thermocouples. 'The 
results have been analysed to give mean values corresponding to clear and 
overcast skies. The greatest values of the temperature differences for each 
month are also given, the maximum values of the lapses found for the lowest 
interval being of the order of one thousand times the dry adiabatic lapse rate. 
Some temperature-height curves for the height interval 2-5 cm. to 
17*1I m. are given, and the time of maximum temperature at various heights 
is discussed. 
