3 1 6 Yapp . — On Stratification in the Vegetation of a 
So, to convert cubic into linear evaporation, it will be necessary to 
multiply the corrected readings (in c.c.), by the following factors : — 
( a ) To convert into centimetres the multiplication factor will be : 
1 _ 1 
i-43 x 141-2 202 
(b) To convert into millimetres : 
10 1 
1.43x141-2 20-2 
(c) To convert into inches : 
1 __ 1 
i -43 x 14 J 2-54 513 
Using the last factor (e), the greatest evaporation for twenty-four hours 
recorded at Wicken Fen in 1908 (i. e. on August 2) by the exposed evapori- 
meter in position A was 0-137 inches. On one occasion this was exceeded 
in 1907 (i. e. on August 1 5), when the evaporation for the same position was 
0-169 inches. Dr. Mill informs me that the highest evaporation from the 
standard tank at Camden Square, London, during the whole of 1908, was 
0-21 inches (on June 5). Also, that on only four days during the whole year 
did the evaporation reach 0-20 inches. 
We may now compare these results with those obtained by Livingston. 
In the desert air at the Arizona Laboratory, the evaporation was of course 
very much greater. The highest recorded by Livingston for any one day 
was 0-504 inches, while the average for twenty-nine days was 0-304 inches. 1 
Methods of calculating Temperature Results. 
The temperature results given in Tables III to V (p. 299) were 
obtained by the following methods : — 
(a) Mean daily temperature. As stated in the main paper, maximum 
and minimum temperature readings were taken each time that the evapora- 
tion was measured. From the data thus obtained, it was not possible 
to calculate the mean daily temperatures by the same methods as those 
employed by meteorologists. 2 The following was the method adopted. 
The mean was first taken of all the day readings for the period in question. 
Then the mean of all the night readings. Finally, the mean of the day and 
night means was found, and this was regarded as the mean daily tem- 
perature. 
(1 b ) Mean of daily maxima. Obtained by taking the means of all the 
absolute maxima for the days in question. The lower maxima from the 
other daily readings were, for this purpose, ignored. 
1 Livingston (’06), p. 29. 
3 Iiann (’03), pp. 7 and 8. 
