NO. 17.] 



CLOUD. 



521 



Cirrus is found most frequently during the day, and least frequently in 

 the early morning hours. 



Cirro-stratus has a less regular period. In winter, summer and autumn, 

 we find a greater amount during the day than during the night; but in spring 

 the period is reversed. 



Cirro-cumulus has a maximum of frequency at 2 p. m., and a minimum 

 about 2 a. m. in all seasons. 



Strato-cumulus has a maximum in the day hours, in spring and sum- 

 mer a couple of hours after noon, in autumn at 10 a. m., and a minimum 

 in the early morning hours, with a rather large range. 



Cumulus has a very slightly pronounced period with a maximum in 

 the middle of the day, and a minimum at midnight. 



Stratum shows a maximum in the early morning hours and a minimum 

 at noon or later in the afternoon. The range is rather large in summer and 

 autumn.. 



66 



