28 VEGETATION OF THE PEAK DISTRICT [CH. 



The readings at 335 metres may be taken as indicating, in a 

 general way, the conditions which prevail at the present upper 

 limit of woodland, in the scrub and grassland associations, and 

 in the heather association. Those at 500 metres may similarly 

 bfe regarded as illustrating the conditions which prevail in 

 the cotton-grass association, and those at 750 metres the con- 

 ditions a little above the bilberry and retrogressive moorland 

 associations. 



It is necessary to point out that most of the readings here 

 reproduced were taken during the afternoons. Hence, as 

 regards temperature, the figures roughly represent maxima. 

 The figures relating to the direction and velocity of the wind 

 may be taken as fairly satisfactory averages of the periods which 

 they represent ; and those relating to the humidity of the air 

 also represent fairly satisfactory averages of readings taken 

 during the daytime. It is obvious that observations are 

 required for many more years before real averages may be 

 deduced ; but, so far as the figures go, some interesting results 

 are indicated. 



Temperatures 



In accordance with expectation, there is a decrease in 

 temperature as the higher altitudes are reached ; but this 

 decrease is greater than would have been predicted by Dalton's 

 rough and ready rule. This rule states that the temperature 

 falls 1° F. for every ascent of 300 feet (91-4 m.). However, 

 fi-om the figures shown on the next page, it may be calculated 

 that, in 1908 and 1909, on the hills of the Peak District, 

 the actual fall of temperature for every ascent of about 

 300 feet was very much greater than this. Of course, many 

 more readings are necessary before any rule, which accurately 

 represents the real phenomenon, can be stated. 



December, January, February, and March are shown by the 

 following tables to be cold months with combined averages of 

 2"6°, 1*8°, and 0*5° C. at the three altitudes respectively, during 

 the two years. May, June, July, August, September, and 

 October are warm months with similar averages of 12*9°, 10*9°, 

 and 8"9° C. ; and November and April are intermediate, with 

 similar averages of 5-9°, 47°, and 27° C. 



The coldest day of 1908 was December 29th, when tem- 

 peratures of - 7-2°, — 7-8°, and — 9*4° C. were registered at the 



