13 



The amount of cloud is greatest during the winter (De- 

 cember January) and least in summer (August). Buchara 

 has 180 bright days per annum; at Petro Alexandrowsk, for 

 instance, the average number of bright days is 17 in June, 

 22 in July, 25 in August, 23 in September and 18 in October 

 (PICKER p. 554), and other places have about the same num- 

 ber. An overcast sky is rare during the summer; thus Petro 

 Alexandrowsk has the low average of about 4 days during 

 the five months June October, and Tashkent about 8 days 

 when the sky is overcast. 



Calm days predominate, and from the records of KERS- 

 NOWSKIJ (p. 108) I have calculated that at Petro Alexandrowsk, 

 27 per ct. of all the observations for the year (which are 

 made 3 times daily) showed calm. During the summer months 

 it was 29 per ct. - The prevailing winds come from the N. 

 and N. E., they average 37 per ct. for the whole year and 41 

 per ct. for the summer months. Less frequently the winds 

 blow 7 from the E. and N. W., while winds from the S, S. E. 

 and S. W. together total at Petro Alexandrowsk only 5 p. ct. 

 during the summer months. The prevailing N. and N. E. 

 w T inds are moreover the strongest, yet only rarely do they 

 attain any great strength; they are also the most constant, 

 and blow especially during spring and summer being accom- 

 panied by bright weather, a cloudless sky and dry air. They 

 are dry in themselves, and as they travel from colder to 

 warmer zones they yield no precipitation, but cause evapora- 

 tion (MUSHKETOW). 



The precipation is slight. In contrast to southern Russia 

 which has summer rain, the precipitation maximum occurs 

 here during the winter or the spring (HANN III p. 192). The 

 winter snow must be of great importance to the vegetation, 

 and as late as April in many places rain cannot be termed 

 rare. July and August are exceedingly dry, in Merw it has 

 not rained at all during these months for four years. When 

 greater quantities of rain fall it is as a few heavy downpours, 

 not continuous rain. The number of rainy days is therefore 

 small, which is of great importance to the plants, because 

 extreme conditions are the result. 



