CLOUDS AND CLOUD-DRIFT 27 



height above the sea-level it appears that the freezing-point 

 of water is reached at an elevation of about 3 miles ; this 

 height is therefore the lower limit of cirrus over Jamaica. 

 As already said, cirras is often seen in the morning about 

 sunrise during the summer and autumn months, but they 

 rapidly disappear as the temperature of the day increases. 

 Under these circumstances they are fine-weather clouds, and 

 it is only when they increase in extent and develop into cirro- 

 stratus that they can be connected with bad weather. 



According to the following table, there is a well-marked 

 upper current from the east-north-east during the autumnal 

 months 



North 



North-east 



East 



South-east 



South 



South-west 



West 



North-west 



100 100 



The numbers given in this table refer to a long series of 

 observations at Kempshot, and express the fact that out of 

 100 observations where the cirrus-drift was observed, 7 times 

 the drift was from the north, 26 times from the north-east, 

 and so on ; and similarly for cirro-stratus. 



The table also shows a still higher current from the west ; 

 and the existence of this current has been confirmed at times 

 by the drift of long continuing trails of shooting-stars, and 

 by the drift of dust from volcanoes in eruption. 



(2) Cirro-stratus. This cloud consists of thin sheets of 

 fibrous texture ; the threads often seem to interlace, when 

 the clouds appear to be woven. Solar halos, mock suns, 

 etc., are caused by the ice particles of which this cloud is 

 composed. Cirro-stratus is always found to surround the 

 advancing half of a cyclone ; and hence its importance in 

 forecasting the weather. The lower limit is the same as 

 that of cirrus ; it also shows the north-east current, but not 

 the hiojhest west current. 



