74 
NATURE FOR ITS OWN SAKE 
Sun and 
moon ha- 
los. 
The cirro- 
cumulus, 
Dappled 
and mack- 
erel skies. 
an altitude of thirty thousand feet, and has a 
maximum travelling velocity of about seventy 
miles an hour. It is the substance from which 
the halos about the sun and moon are woven, 
and is very thin, almost transparent. Like the 
cirrus, it casts no patches of shadow, is pale 
white, and when struck from beneath by the 
rays of the sun below the horizon is marvellous 
in its delicacy of light and color. 
The ctrro-cumulus (b) is another mixed 
cloud. When the cirrus descends still lower 
than the region of the cirro-stratus, its edges 
of frost begin to melt like the sharp sides of a 
snow-bank. It then takes on a woolly appear- 
ance similar at times to the small, detached 
portions of true cumulus, though it lies in a 
much higher field of air. It has a fashion of 
breaking up into small, rounded patches like 
rotten ice in ariver, and of drifting across the 
sky in vast companies that almost hide the 
blue. There are two forms in which it ap- 
pears. One is called the ‘dappled sky” or 
sometimes “ wool- pack” from its fleecy nat- 
ure; the other is the “mackerel sky,” which 
is not fleecy but hard-looking. The latter is 
rarely seen as compared with other cloud forms, 
and in England it is always thought to be the 
