30 CONTRIBUTIONS TO THE NATURAL HISTORY OF ALASKA. 



at a time. Stratus and nimbus are so intimately related that to separate them would add con- 

 fusion, and I have used the term nimbus for an actual raiuing-cloud. From these two kinds the 

 greater part of the precipitation falls, excepting the finest particles of snow. 



CUMULO-STRATUS. 



Cumulo-stratus, attendant upon the warmest days of summer, is the most prevalent cloud 

 during that season, and attains the magnitude it does in warmer latitudes. Far in the edge of 

 the east or south horizon, several small, firmly-outlined clouds will expand to overspread the 

 greater part of the heavens by 2 p. m., and from these the most copious showers of rain fall. The 

 height of this cloud is from 2,000 feet to about 2 miles, usually of blue color and white edges. 



CUMULUS. 



Cumuli are classed as belonging to the lower system of clouds, and rarely present any other 

 appearance than extraordinary cumulo-stratus. But few distinctions have been made in the daily 

 journal between these two clouds. 



True cumuli rarely approach nearer than 6 to 10 miles, and more often the heads of the 

 clouds are but little raised above the horizon. These clouds are principally formed in the south- 

 east and west-southwest. 



I noticed rain to pour from one of these clouds in June, 1875, for several hours on the main- 

 land, about 20 miles distant, and accompanied by thunder and lightning. 



The usual color is dark blue to bright indigo, and occasionally silver-edged. 



CIRRO-STRATUS. 



Cirro-stratus is not often observed, and is usually the result of rapidly descending cirri. 

 Stratus and cirro-stratus are at times scarcely distinguishable. Snow in finest, round, firm rifts 

 form this cloud in winter. The usual color is grayish. 



PALLIO-CIRRUS.' 



This cloud forms itself in such an incredibly short time as to give but little time for its study . 

 it disappears as suddenly. Usually perfect, and really an exaggerated form of low globular cirro- 

 cumulus, rarely moves from any other point than north or south, and is almost certain to result 

 in snow. It seldom remains longer than three hours, and but once hung for three days, this sel- 

 dom attaining sufficient density to veil the sun, and presents that singular phenomenon of sunshine 

 and clouds. It has a pale-blue rounded form and white-edged, seemingly in a state of repulsion. 



-CIRRO-CUMULI. 



The prevailing forms of this cloud are the apparent converging bauds, often of the greatest 

 delicacy of texture. 



On one occasion eleven perfect bands were seen, and four to seven being common. These 

 bauds usually extend due east and west, moving from south, rarely from north; and northwest 

 and southeast, moving from northwest, rarer still north and south, moving from either point, 

 though more frequently from south 5 and southwest and northeast from either point, though most 

 frequently from northeast. 



These bands most often extending east and west is probably due to the indrawing effect of 

 the ascending and descending currents near this latitude. 



Broken bands and irregular forms are common. One of these irregular forms is like a wall of 

 masonry with the mortar left out, and, if in the east or west near the time of sunrise or sunset, it 

 is most beautifully tinted with a rather deep pink, forming a splendid spectacle. 



The cirro-cumulus cloud has a great range through the atmosphere of probably 1 to 4 miles. 

 Their color is usually pale pearly-blue to white. 



