222 J. HOPKINSOX THE CLrMATE OF ST. ALBANS. 



below freezing-point in May — on the 7tli of May, 1892. The 

 average number of fi'osty nights (not including ground-frosts) has 

 been as follows : — 



Temperatures above 62° have occurred in every month but the 

 three months of winter. Only twice has the temperature been 

 above 62° in November — on the 1st of jS'ovember, 1894, and on the 

 16th of November, 1895. The average number of days on which 

 the maximum temperature has exceeded 62° has been as follows : — 



July 28 Oct. 2 



August 27 JMov. 



Sept. 18 Dec. 



The minimum temperature has been below 1 2° on five nights 

 during the whole period — 24th December, 1891, 6th January, 

 1894, and 6th, 7th, and 8th February, 1895. The maximum has 

 been above 82° on 26 days in all — on one day in May (."iOth May, 

 1895), seven days in June, nine days in July, and nine days in 

 August; fifteen of these 2() days were in 1893. 



The minimum temperature of the year has occurred three times 

 in January, four times in February, and three times in December ; 

 the maximum has occurred once in May, once in June, three times 

 in July, four times in August, and once in September. 



Temperature, Humidity, and Cloud at 9 a.m. (Tables YII-IX, 

 p. 223). — The temperature of the air in these tables is that 

 shown by the dry-bulb thermometer, the temperature of evaporation 

 that shown by the wet-bulb. From these values the temperature 

 of the dew-point, or that at which dew would be deposited, is 

 calculated. The thermometric dryness is the difference between 

 the temperature of the air and that of the dew-point ; the relative 

 humidity is the percentage of moisture in the air to its complete 

 saturation, represented as 100. 



The mean temperature at about 9 a.m. is on the average 0°*5 

 lower than the mean of the minimum and maximum temperatures ; 

 in no year has the difference exceeded 0°-8. (The observations 

 have as a rule been taken a few minutes before nine, which probably 

 accounts in some measure for the discrepancy of about half a degree 

 between these and the "Watford observations.) 



From January to April, and from September to December, the 

 temperature at about 9 a.m. is appreciably lower than the mean of 

 the mimimum and maximum ; in May it is a little higher, and 

 from June to August (the three summer months) it is about the 

 same. The mean of the 9 a.m., the minimum, and the maximum 

 temperatures, probably gives a truer mean for the day than does 

 the mean of the minimum and maximum alone. If this be the 

 case the mean diurnal temperature in the first and last four months 

 in the year is probably rather lower than that given in Table VI, 

 and in May rather higher, the mean being true for the summer 

 months, while for the year it would be 47°'8. 



