360 
POPULAR SCIENCE REVIEW. 
This species, alluded to by Sir John Herschell in his “ Fa- 
miliar Lectures on Science,” cannot be regarded as so strictly a 
cumulus as the form we have just remarked upon, inasmuch as 
it exhibits at times a great tendency to the form of stratus, 
and at other times to that of cirrus ; or, perhaps we should 
rather say to the form of cumulo-cirrus.* As an indicator of 
wind, this cloud may probably be regarded as unrivalled. It 
frequently appears two or three days before heavy gales, es- 
pecially when they are of long duration, as about the Equinoxes. 
Without being hyper-critical, or, I should say, hyper-analytical, 
we may distinguish three varieties of the cloud, the distinction 
between the outlines of which is quite characteristic. The first 
variety possesses greater affinity for ordinary cumulus than the 
other two, and it often shows great resemblance in many points 
to the electric cumulus. It occurs for the most part in large 
masses, or banks, the summits of which, as it drifts along with 
the wind, stand out in sharp relief against the upper sky, and 
exhibit the most striking and fantastic resemblances to terrestrial 
objects, beetling crags, towers, and heads of animals — the last 
being of frequent occurrence. When of this variety, the Anvil 
Cloud appears to be highly condensed, and is of a dark blueish 
or slatey tint. It is generally, I believe, the precursor of heavy 
rain as well as wind. 
The second variety of the cloud, which approaches to stratus, 
exhibits a more irregularly formed “ anvil,” the “ waist ” being 
usually much more conspicuous on one side than on the other. 
This is also a dense cloud, without much marking on its 
surface, the outline being not nearly so irregular as that of the 
variety just described. It is of a lighter tint, grey or muddy 
blueish, and does not, I think, occur in an isolated form, but 
rises from a bank of lower stratus or cumulo-stratus. It is also 
a wet-weather cloud. 
The third variety is apparently much thinner in texture 
than the two preceding, being, however, of a double character : 
cirrus in the upper part, condensed cumulus, or cumulo-stratus 
in the lower. This is the least common of all three varieties, 
but is an excellent indicator of wind. 
There is another form of cloud which has a close affinity for 
this last-mentioned species ; a kind of aggregated cirrus, gene- 
rally of a dark tint and seen at high altitudes, in windy weather. 
This lacks the consistency and volume of cumulus, and mostly 
spreads itself out in a sheet, with rounded edges, and without 
surface marking ; whereas the third form of anvil cumulus ex- 
* This cloud, also an excellent indicator of wind, does not appear to have 
received the attention it deserves from meteorologists. The reader must 
not confound it with cirro-cumulus. 
