31 



weather is essential to the formation of the Stratus ; it is 

 frequent in fine autumnal nights and mornings, sometimes 

 resting on the ground, sometimes hovering some hundred 

 feet above it. It obscures the sun until his rays have raised 

 the temperature of the air sufficiently to evaporate it, 

 when it gradually disappears and leaves a clear blue sky. 

 The Stratus deposits moisture : and when the tempera- 

 ture, from radiation or other causes, sinks below 32^, 

 we find it fettered in icy spicula? upon trees and shrubs, 

 and sparkling in exquisite frostwork upon all nature. 



The Stratus is called the night cloud, and is most 

 frequent from September till January. It has no sen- 

 sible effect on the barometer. 



Scud is, with the exception of the Stratus, the lowest 

 cloud. It is most commonly seen during the winter 

 months, with every wind that blows and with all press- 

 ures of the atmosphere. It always moves in the direc- 

 tion of the wind, and apparently with great rapidity. 

 It is more frequently seen after rain than at any other 

 period. In our westerly gales in winter, it continues 

 for days together, deforming the sky with its large, 

 loose, shapeless masses. 



It is not uncommon to observe two or three strata of 

 clouds moving in different directions ; the lowest follows 

 the direction of the wind blowing at the time near the 

 surface of the earth ; the upper strata follow the cur- 

 rents in the upper regions of the atmosphere ; which may 

 be in opposite directions. Before thunder and heavy 

 rain this is of usual occurrence, the barometer at the 

 time being low or in a falling state. 



