228 J. HOPKINSOX THE CLIMATE OF WATFOKD. 



maximum alone. The mean diurnal temperature from Novem- 

 ber to March is therefore probably rather lower than that given 

 in Table VI, and from April to August rather higher. 



The spring and summer half of the year is much drier than 

 the autumn and winter half, having on the average 12 per cent, 

 less relative humidity. Summer is drier than spring, by 2 per 

 cent. ; autumn is drier than winter, by 4 per cent. Spring, 

 summer, and autumn are about equally cloudy, and much less 

 so than winter. Summer and winter have fewer days of clear 

 sky than spring and autumn ; spring and summer have fewer 

 days of overcast sky than autumn, and autumn has much fewer 

 than winter. 



The air is driest in May and most humid in December and 

 January, June and July closely following upon May in dryness, 

 and November and February closely following upon December 

 and January in dampness. Though the coldest months are the 

 most humid, the warmest are not the driest, for the three 

 summer months are more humid than May, and September is 

 much more humid than April. March is an exception to this 

 rule, being a cold and rather dry month. 



December, January, and February are much more cloudy than 

 any other months in the year. March has the greatest number 

 of days of clear sky, February the least ; January has the greatest 

 number of days of overcast sky, May the least. 



Force and Direction of the Wind at 9 a.m. (Tables X-XII, 

 p. 229). — The force of the wind, like the amount of cloud, is 

 arrived at by estimation, but while it is easy to estimate the 

 proportion, in tenths, of cloud to clear sky, it is not easy to 

 estimate the proportionate force of the wind, from calm, repre- 

 sented by 0, to a hurricane such as we never experience in this 

 country, represented by 12. The greatest force on this scale at 

 which I have ever estimated the wind at 9 a.m. is 7, on two 

 occasions ; the greatest estimated mean force in any month is 

 3-0 (in April, 1881); the least in any month is 1-0 (in February 

 and November, 1886). The mean annual force has varied from 

 1'6 to 2 0. The wind is strongest in spring, lightest in summer, 

 and rather stronger in autumn than in winter, but the mean 

 seasonal variation is very slight. It is strongest in April and 

 lightest in July. 



With regard to direction, S.W. winds are much the most 

 prevalent, and E. winds are the least so. The wind has been 

 S.W. on as many as 95 days in the year, and it has been S.E, 

 on as few as 17 ; both these extremes were in 1877. S.W. winds 

 prevail most in summer, and are less prevalent in spring than in 

 autumn or winter ; N.E. winds prevail most in spring. There is 

 no great preponderance of winds from any other quarter in any 

 season. S.W. winds prevail most in July and August, N.E. winds 

 most in April and May. There are very few E. winds in February, 

 July, November, and December. Calms occur most often in 

 December ; much the least often in April and May. 



