2. Humidity.—­The relative humidity of the air, that is the amount of moisture it contains short of complete saturation which is represented by 100, is, at 9 A.M., 82.  It has varied from 78 in 1893 to 85 in 1888 and 1889.  The air is much drier in spring and summer (78 and 75) than it is in autumn and winter (86 and 89).  There is the least amount of moisture in the air from April to August (74 to 78), and the greatest from November to January (90).

3. Cloud.—­The mean amount of cloud at 9 A.M., from 0 (clear sky) to 10 (completely overcast), is 6.7.  It has varied from 6.0 in 1893 to 7.4 in 1888.  Spring, summer, and autumn are about equally cloudy (6.5 to 6.6), and winter is considerably more so (7.2).  The sky at 9 A.M. is brightest in September (6.0) and most cloudy in November and January (7.5).

4. Sunshine.—­At Berkhampstead only have records of bright sunshine been taken for the whole of the twelve years.  Throughout the year the sun shines brightly there for nearly four hours a day (3.9).  The average duration in spring is 5.0, in summer 5.8, in autumn 3.2, and in winter 1.6.  The duration is least in December and greatest in May; the sun shining for rather more than an hour a day in December and nearly six hours and a half in May.  An apparent discrepancy between this and the preceding section is due to a bright day often following a cloudy morning and vice versa.

5. Wind.—­The prevailing direction of the wind, as recorded at Berkhampstead, St. Albans and Bennington, is from S.W. (sixty-one days in the year) to W. (sixty-two days), and the next most frequent winds are N. to N.E. and S. (each about thirty-seven days).  The least frequent are S.E. (twenty-five days).  About forty-four days in the year are recorded as calm.

6. Rainfall.—­Twelve years is much too short a period to give a trustworthy mean for such a variable element of climate as rainfall, and five stations are much too few to deduce an average from for Hertfordshire.  The average rainfall at a varying number of stations for the sixty years 1840 to 1899 (from one station in the first decade of this period to twenty stations in the last decade) was 26.15 inches.  In the driest year (1854) 17.67 inches fell, and in the wettest (1852) 37.57 inches.  Spring has 5.40 inches, summer 6.97, autumn 7.87, and winter 5.91.  The driest months are February and March, each with a mean of 1.65 inch; April is but very little wetter, having 1.69.  The wettest month is October, with 2.96 inches, and the next is November with 2.56.  The mean number of days of rain in the year, that is of days on which at least 0.01 inch fell, for the thirty years 1870-99, was 167.  Autumn and winter have each about six more wet days than spring and summer.  The rainfall is greatly affected by the form of the ground, the southern and western hills attracting the rain, which chiefly comes from the S.W., so greatly that with a mean annual fall of about 26 inches there is a difference of 31/2 inches between that of the river-basin of the Colne on the W. and that of the river-basin of the Lea on the E., the former having 28 inches and the latter 241/2.  The small portion of the river-basin of the Great Ouse which is within our area has rather less rain than the average for the county.