us, which is
rapidly condensing, and turning to stratus. In the "mackerel sky,"
strictly so called, the waves are small, parallel, nearly distinct and
equi-distant, and resembling the appearance of a school of mackerel,
swimming in the same direction, one above another. All _wavy_ forms of
cirro-stratus indicate a disposition to increased condensation and rain.
When the waves are very large and dense, and cross obliquely, or unite at
one end, rain is very certain to fall soon, if the line of progress of the
condensation is over the observer, and the clouds are seen in the western
or N. W. quarter of the sky.

But there are few forms which are not occasionally seen when no rain or
snow falls. The intensity of the electric action which produces them may
not be sufficient to effect precipitation, or they may be the attendant,
attenuated _lateral_ condensation, which frequently "thins out" a
considerable distance from the dense, precipitating portions of the storm.

If that denser portion is north of us, the probabilities of rain are
greater, for there is always a probability that the storm may be of the
character which is extended south, by a polar wave. The observer must
watch the formation of cirri, and the different forms of cirro-stratus and
stratus, and become familiar with their appearance. It is not a difficult
task. With the aid of a few general directions he will soon be familiar
with them:

1. Get a correct idea of the different characters of the primary clouds.
The true fibrous _cirrus_--the different forms of _cirro-stratus_--the
smooth, uniform _stratus_--the _cirro-cumulus_, which is nothing but a
cirro-stratus, separated into _distinct masses_ by the repulsion of static
electricity--and the _cumulus_, too distinct ever to be mistaken. There is
no difficulty, except with the varied forms of cirro-stratus. It is
useless to attempt to give, or the observer to rely on, names for these
numerous forms, without as numerous illustrations. Those in use are rarely
applied correctly. I have never met with ten persons who applied even the
term "mackerel sky" to the same precise form of cirro-stratus. In relation
to all of them it is to be observed that polar belts of condensation, and
local appearances of considerable extent, are often too feeble in action
to precipitate, even when the mackerel form is present; and all may be the
lateral attendants of passing storms. Therefore,

2. Satisfy yourself whether the cirrus