120 SCIENCE AND FRUIT GROWING 



particular occasion may be considerable : with the maximum 

 and minimum air temperatures, and with the minimum radiation 

 temperatures, differences of 5 F. were sometimes noticed, and 

 with the earth temperatures the extreme differences were rather 

 greater; but when the averages for the twenty years are con- 

 sidered, the differences are by no means large. The average 

 maximum air temperatures at the two stations are identical 

 for the winter months, and the difference between them reaches 

 its highest value in the summer, the temperature at the upper 

 station being then the lower to the extent of o'5 : the difference 

 is nearly as great in the autumn (0*47), but less in the spring 

 (o'3i). Whilst the upper station is the cooler as regards the 

 maximum temperatures, it is the warmer as regards the minimum 

 temperatures, the differences in these being greatest in summer 

 and autumn (o'68 and 0*78), and least in the winter and spring 

 (o'3i and 0*37). In no single month are the differences in 

 the opposite direction. Thus, the variation of air temperature 

 is less at the upper than at the lower station to the average 

 extent of 



Winter. Spring. Summer. Autumn. 



0-31 0-68 1-18 1-25 



Whilst the average values for the air temperatures at the two 

 stations show such close agreement, it is only very rarely that 

 the readings at the two are identical. The results for fourteen 

 years, up to 1909, were examined from this point of view, and 

 out of the 10,220 sets of readings taken during that period, 

 identity was found on only fifteen occasions, representing 

 0*15 per cent, of the total. 1 



The air temperatures are shown graphically, together with 

 other data, in Fig. 17, where the readings at the lower station are 

 represented by the horizontal lines at o, and those at the higher 

 station by the curved figures. As regards the maximum and 

 minimum air temperatures, the values are fairly complementary 

 of each other, the monthly readings in both cases showing 

 considerable regularity in the variation throughout the year. 



1 Observations at different levels have been made at other observatories, 

 and the results may be found at the Meteorological Office, London. 

 Camden Town : 4 and 20 ft. ; 1867-1872. 

 Oxford : 5 and 105 ft.; 1862-1908. 

 Greenwich : 4, 22 and 50 ft. ; six wee'ks in 1868. 

 Kew : 22, 69 and 129 ft.; 1873-1875. 

 Greenwich : 4 and 20 ft. ; 1886-1909. 

 Peel House : 6, 52 and 86 ft.; 1872-1874. 

 Berlin : 1909. 



