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POPULAR SCIENCE REVIEW. 
to interchange their places in regard to altitude ; that is to say 
cumulus rises to an abnormal height, and cirrus descends to an 
unusually low position. This may generally be verified by 
watching the course of a thunderstorm ; when the peaks of the 
first-mentioned cloud may often be observed, at a great distance, 
thrusting their pale yellow pinnacles into the azure of the 
heavens, long before the first muttering of the storm is heard, 
and while the mass of cloud is far beyond the horizon. On the 
other hand, when the hurly-burly is over and the rain has ceased, 
masses of nimbo-cirrus may at times be seen throwing up their 
silvery crests and curling over the earth like gigantic breakers. 
This last-mentioned appearance, which has a splendid effect, is, 
I believe, never seen except in thundery weather, or rather 
during electrical disturbance, and it is not easy to account for 
the existence of such forms by the action of wind. This remark 
applies also to what we may call “ star ” cirrus ; that is, cirrus 
streaks radiating from a common centre in all directions (a form 
of cloud also connected with thunder-storms) ; and to that form 
which resembles the feathering of an arrow — parallel rays run- 
ning from both sides of a common axis. 
