THE CLIMATE OF YORK 



19 



readings referred to the 24 hours ended 8 h., while during the last 30 years 

 they referred to the 24 hours ended 21 h. As they stand, however, the 

 figures accord with the general belief that our winter climate has become 

 milder — a conclusion which is supported by other statistical evidence. 



Humidity, 



The data of Table HI are based on daily observations of dry and wet bulb 

 thermometers in a Stevenson screen at gh. and 21 h. during the ten years 

 1921-30. On the basis of the results obtained at our observatories it 

 may be assumed that the average of the readings at gh. and 21 h. agrees 

 within about 2 per cent, with the average for the whole day, in all months. 



Table HI. — Humidity. 



The yearly means are almost identical with those for Kew Observatory, 

 Richmond, Surrey, and the annual variation is very similar. It may be 

 said, in fact, that in regard to relative humidity the York figures are typical 

 of those usually obtained at low-lying inland stations. 



Relative humidity is an element subject to a large diurnal variation, 

 and we cannot, therefore, regard mean values for the day, or at fixed hours 

 in the morning and evening, as giving a complete statement in regard to 

 this important climatic factor. It is possible, however, to arrive at an 

 approximation to the mean diurnal minimum of relative humidity by taking 

 advantage of two well-known facts : (a) that the minimum relative 

 humidity occurs, on the average, at the same time as the maximum 



