CHAP. 2. 1. OF CLOUDS. 43 



cirrus, which is seen in the intervals of the rain, 

 is ill defined, and often of a sort of plumose 

 figure; and it has less of the fibrous structure: 

 this may be attributed to its being surrounded 

 with moister air, which being a conductor, 

 though an imperfect one, there is not the same 

 necessity for the cirrus to be drawn out into 

 fine transmitting points; as the fluid can fly off 

 more generally from all parts of it. Cirri of 

 this kind are generally of short duration, and 

 have a great tendency to change into the other 

 modifications; there is often a haziness in the 

 atmosphere when they appear, and they are 

 frequently soon followed by Rain. They seldom 

 appear in fair dry weather; and if cirri, which 

 have been previously fibrous, put on the plumose 

 and indefinite character, a change to wet weather 

 may be expected. All these are circumstances 

 which corroborate the opinion, that the humidity 

 of the circumjacent air is the cause of this kind 

 of feature of the cirrus, and agree very well with 

 the nature of the office already assigned to it. 



I have almost always found the fibrous cirri 

 to be accompanied by dry air. But there are 

 rare exceptions to this rule. The upper air 

 may, however, be tolerably dry, while the under 

 air is moister, which may account for the occa- 



