78 
NATURE FOR ITS OWN SAKE 
Cloud illu- 
stons. 
Gold and 
silver lin- 
ings. 
oracrossthem. In outline they are graceful, and 
in light-and-shade they are often sharp-marked. 
The best time to study them is in the evening, 
when they are lying back at the south or east. 
Then the pinnacles and peaks glow with light, 
and make the snowy-mountain illusion more 
palpable than ever ; or they turn into phantom, 
rock-based promontories with spectral tides of 
vapor at their feet that sound not and shock 
not, yet rise slowly higher and higher upon the 
snowy walls. Occasionally a tall, heavy mass is 
veiled by a thin layer of the stratus, through 
which the form of the cumulus is scen to burn 
‘\like a great opal. Sometimes, too, a heavy 
cumulus is seen through city smoke at sunset 
glowing like molten metal. When in the west 
and in front of the sun this clond is the one 
that shows us the gold or silver lining ; and 
under sunset light it is possible for it to take 
on all tints and shades. When it is not near 
the sun but les off at the side, we often see the 
pink, ‘‘ Alpine glow” suffusing the white cas- 
tellated tops ; and the shadows caused by sharp 
breaks of form often show blue, lilac, and even 
pale green in hue. 
The cumulo-nimbus (a) is substantially the 
same cloud as the cumulus except that it drifts 
