METEOROLOGICAL OBSERVATIONS AT WISLEY, 1915. 123 
survey no excess or deficit in either of the elements of climate with 
which we are concerned stands out with special prominence, and the 
year as a whole takes its place after all as a fairly normal one. 
January. — Throughout the greater part of the month the weather 
was continuously rough and windy, and so extremely wet as to interfere 
very materially with outdoor operations in the garden. Weather of 
this type in the British Isles is usually due, as was the case now, to a 
succession of cyclonic disturbances moving along a more or less north- 
easterly track lying either just beyond our western coasts or across 
the northern portion of the kingdom. Such systems are accompanied 
by a definite wind circulation which over their southern section is 
southerly or westerly ; and as at this season of the year these winds 
are relatively warm as well as wet the temperature was generally above 
the average for January. At Wisley the thermometer occasionally 
rose above 50 0 , and rarely failed to exceed 40 0 as the maximum of 
the day ; and neither there nor in any part of the kingdom was there 
a continuous frost. About the close of the third week, however, there 
was a sharp " cold snap " of very brief duration, accompanying 
which was a considerable fall of snow over south-eastern England, where 
in some parts its depth amounted to a foot ; but it was the only fall 
of snow worth mentioning, and it disappeared very quickly. The 
rainfall of the month exceeded the average over practically the whole 
of England and Wales, but more especially over the southern counties ; 
there were districts in Ireland and Scotland where it was less than 
the average. As the large rainfall followed upon an equally abnormal 
excess of rain in December, it is not surprising that there were large 
floods in the Thames Valley and elsewhere, the level of the water in 
the Thames being higher than for the preceding twenty years ; whilst 
intermittent springs, as the " Croydon Bourne," broke out with quite 
remarkable volume. The amount of bright sunshine was small, and 
averaged less than an hour and a half a day at Wisley. 
The results obtained from the observations made at Wisley are 
shown in the following table : 
Mean temperature of the air in shade 
Highest 
Lowest 
„ „ on the grass 
Number of nights of ground frost 
Mean temperature of the soil at 9 a.m. 
Highest 
Lowest „ 
• 39-4° 
. 53-3° on the 13th 
. 21-8° „ 23rd 
• 177° » 3°th 
18 
At depth of 
1 ft. 2 ft. 4 ft. 
39-2° 4 i-4° 43-7° 
43'7° 43-7° 44-8° 
35-9° 38-8° 42-0° 
Mean relative humidity of the air at 9 a.m. (complete saturation being repre- 
sented by 100), 88 per cent. 
Rain fell on 19 days, to the total depth of 4-19 in. (equivalent to about 19! 
gallons of water to the square yard). Heaviest fall on any day 1-18 in., on the 
22nd. 
The prevailing winds were south-westerly. 
The average velocity of the wind was 7^ miles an hour. 
There were 45 hours of bright sunshine, equal to 18 per cent, of the greatest 
possible amount. 
There were 17 days on which no sunshine was recorded. 
