28 VEGETATION OF THE PEAK DISTRICT [cH. 
The readings at 335 metres may be taken as indicating, ina 
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 
be 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, 
from 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°, 18°, 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 2°7°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 
