42 PHYSIOGRAPHY. [chap. 



fact, absorbed by the atmosphere; and the drier and 

 hotter the air happens to be, the more greedily does it 

 drink up this moisture. 



Again, if a current of warm and moist air meet a colder 

 current, its temperature is reduced, and more or less of 

 its moisture is deposited. In this country, the south-west 

 winds, having swept over the warm waters of the Atlantic, 

 are charged with moisture, and ready to deposit a portion 

 of their freight whenever they are sufficiently chilled, as 

 they may be, for example, by meeting a cold east wind. 

 Hence south-west winds act as the chief rainbearers to 

 our islands. 



So fantastic and varied are the forms presented by clouds 

 that they seem, at first sight, to defy scientific classification. 

 In 1802, however, Mr. Luke Howard, an eminent meteoro- 

 logist, proposed, in an essay On the Modifications of Clouds, 

 a system of nomenclature and classification, which has 

 since been so commonly adopted that his terms are frequently 

 used, even in popular descriptions of scenery. Reference 

 to Plate III. will convey a better idea of the typical forms of 

 clouds than could be got from any long technical descriptions.' 



Delicate white fleecy clouds may often be seen floating 

 in the upper regions of the atmosphere, where they are 

 arranged in groups running in more or less parallel directions. 

 Frequently a cloud of this class will present the appearance 

 of hair, or feather, with its fibres curled, and hence it has 

 received the name of cirrusP- The cirrus clouds are always 

 lofty, sometimes as much as ten miles above the surface of 

 the earth; and, being wafted along by currents in the upper 

 regions of the atmosphere, they may often be seen to move in 



1 These figures are partly taken from Instruciions in the Use of 

 Meteorological Instruments, by R. H. Scott, M.A., F.R.S. 1875, 

 ^ Cirrus, a curl. 



