METEOROLOGICAL OBSERVATIONS MADE AT WISLEY. 49 



occurring upon the ground at Wisley during the nights of the 28th to the 

 30th. The low temperature of this period balanced to a large extent 

 the unusual warmth which had preceded it, with the result that the 

 mean temperature for the whole month was very nearly normal. There 

 were no exceptionally strong winds during the month ; but fog was 

 not infrequent, and there was a deficiency of sunshine over the King- 

 dom generally which was especially marked over the eastern half of 

 Great Britain. At Wisley no sunshine was recorded on twenty days, 

 and in London the total record for the entire month was only nine 

 and a half hours, or less than half the usual amount. Rainfall on the 

 other hand was unusually abundant everywhere except in the extreme 

 north and west. At Wisley a measurable amount fell on 17 days, and 

 the total fall slightly exceeded three inches ; but over the entire 

 Thames valley the fall ranged from about three and a half inches to 

 five inches, which is roughly speaking 50 per cent, in excess of the 

 usual amount. A peculiar phenomenon known as ' glazed frost ' 

 occurred on the 17th and 18th, when a gentle rain froze as it fell 

 and trees, shrubs, grass, and also telephone wires, fences, etc. became 

 coated with transparent ice to such an extent that large branches of 

 trees were broken off owing to the weight of their icy casing ; it 

 was curious to notice that the ground itself was not frozen at 

 the same time that the stalks of coarse grass were each coated 

 with a sheath of clear ice, through which the stalk was seen standing 

 erect. 



The results obtained from the observations taken at the Climato- 

 logical Observatory in the Garden at Wisley are shown in the following 

 table : 



January. 



Mean temperature of the air in shade . . 39 7 0 

 Highest temperature of the air in shade . 51*5° on the 6th 

 Lowest temperature of the air in shade . i8*i° on the 29th 

 Lowest temperature on the grass . . . 8*5° on the 29th 

 Number of nights of ground frost . . .16 



At depth of 

 1 ft. 2 ft. 4 ft. 



Mean temperature of the soil at 9 a.m. . 41-5° 42*6° 45-5° 

 Highest temperature of the soil at 9 a.m. 46*0° 45*1° 46-6° 

 Lowest temperature of the soil at 9 a.m. 34'8° 38 o° 43 -4° 



Mean relative humidity of the air at 9 a.m. (complete saturation 

 being represented by 100), 92%. 



Rain fell on 17 days, to the total depth of 3-03 inches (equivalent 

 to about 14 gallons of water to the square yard). Heaviest fall on 

 any day 0*47 inch, on the 17th. 



The prevailing winds were south-westerly. 



The average velocity of the wind was 5 J miles an hour. 



There were 36 hours of bright sunshine, equal to 14 per cent, of 

 the greatest possible amount. 



There were 20 days on which no sunshine was recorded. 



VOL. XXXIX. £ 



