CHAP. 2. L OP CLOUDS. . 47 



direction very different from the direction of 

 their tails: besides, the cirrus has been observed 

 to continue moving on, in the same direction, 

 while the tails have veered round toward 

 another quarter.* 



There is sometimes a kind of motion observ- 

 able in the cirris, which I have never noticed in 

 any other cloud, which it is somewhat difficult 

 to describe, and which, whenever I have seen 

 it, has happened in a cirrus of a particular kind ; 

 namely, in one which has a sort of plumose 

 extremity, with a long fibrous body, and a fine 

 transmitting pointed tail.f The plumose head, 

 which under these circumstances is clearer and 

 rather more fibrous than usual, together with 

 the body, seem all in motion, as if every particle 

 was alive. This motion may be compared to 

 that of a piece of cheese full of mites, which 

 seems agitated in every point, without ever 

 materially changing its place. This was re- 



* Whether by the fleeces of wool, which Aratus, Virgil, 

 and Lucretius speak of, as being carried across the welkin in 

 rainy weather, were intended these comoid cirri, cirrostrati, 

 cirrocumuli, or large flocky scud, is uncertain. They intended, 

 however, to describe the peculiar clouds which accompany 

 variable weather. 



t Plate I. Fig. 2. 



