172 THE ANDES OF SOUTHERN PERU 



spectively. The absolute minimum for the two years was - 22° C. 

 July of 1908 and June of 1909 are also the months of smallest 

 diurnal variability, showing that the winter temperatures are 

 maintained with great regularity. Like all tropical high-level sta- 

 tions, Morococha exhibits winter maxima that are very high as 

 compared with the winter maxima of the temperate zone. In both 

 June and July of 1908 and 1909 the maximum was maintained for 

 about a week above 55° F. (12.8° C), and in 1909 above 60° F. 

 (15.6° C), the mean maximum for the year being only 4.7° F. 

 higher. For equal periods, however, the maxima fell to levels 

 about 10° F. below those for the period from December to 

 May, 1908. 



It is noteworthy that the lowest maximum for 1909 was in 

 October, 44° F. (6.7° C.) ; and that other low maxima but little 

 above those of June and July occur in almost all the other months 

 of the year. While 1909 was in this respect an exceptional year, 

 it nevertheless illustrates a fact that may occur in any month of 

 any year. Its occurrence is generally associated with cloudiness. 

 One of the best examples of this is found in the January maximum 

 curve for 1909, where in a few days the maxima fell 12° F. Cloud 

 records are absent, hence a direct comparison cannot be made, but 

 a comparison of the maximum temperature curve with the graphic 

 representation of mean monthly rainfall, will emphasize this rela- 

 tion of temperature and cloudiness. February was the wettest 

 month of both 1908 and 1909. In sympathy with this is the large 

 and sharp drop from the January level of the maxima — the highest 

 for the year — to the February level. The mean temperatures are 

 affected to a less degree because the cloudiness retards night radia- 

 tion of heat, thus elevating the maxima. Thus in 1908 the lowest 

 minimum for both January and February was 28.4° F. ( — 2° C.). 

 For 1909 the minima for January and February were 27.5° F. 

 (—2.5° C.) and 29.3° F. (—1.5° C.) respectively. 



The extent to which high minima may hold up the mean tem- 

 perature is shown by the fact that the mean monthly tempera- 

 ture for January, 1908, was lower than for February. Single 

 instances illustrate this relation equally well. For example, on 



