194 The Ottawa Naturalist. 



Cumulus. — That form which is the most easily distin- 

 guished and is at the same time also the most beautiful, is 

 known as the Cumulus. These are the dome-like clouds that 

 appear on a showery afternoon of summer, which are commonly 

 called " Thunder heads." They usually rise from a flat base, 

 perhaps a mile above the earth to a height of several thousand 

 feet higher, with bold rounded tops often resembling huge 

 mountains. Where the sun shines upon them they present a 

 fleecy appearance, where it does not, they are dark and frowning- 

 When the opposite side from the observer is exposed to the sun 

 they show most beautifnl white margins being in poetic imagery 

 the clouds with silver lining. 



Stratus. — Stratus includes all low-lying cloud sheets 

 which have no definite form, from the fogs at the surface of the 

 earth, to clouds of considerable height. It is not a cloud of 

 beauty, but is a usual accompaniment of dull weather and 

 cyclonic storms. It is sometimes the only cloud seen at a 

 single point for several days. 



Cirrus. — Cirrus is the name applied to clouds composed 

 of long slender fibres, which are sometimes delicately ; at others, 

 finely banded. They are the highest clouds we see, probably 

 ranging from five to eight or even ten miles in height. In our 

 latitude they generally more eastward, often with a velocity of 

 more than one hundred miles per hour, but owing to their great 

 altitude, they appear to move much more slowly. They un- 

 doubtedly consist of icy particles similar to those which float in 

 the lower atmosphere in our coldest weather. 



CirrO-Stratus. — Cirro-Stratus clouds consist of wavy 

 cirrus fibres mingled with bands of a more horizontal appearance. 

 They often extend across the entire sky, when they converge at 

 opposite points of the horizon and form the peculiar feature 

 known as " Noah's Ark." This is probably due to the perspec- 

 tive effect of the parallel bands seen directly overhead being 

 produced in opposite directions in parallel lines. They range 

 next in height to the cirrus and like clouds of that class are in 

 general an indication of a j:torm. 



