A Guide To The Scientific Knowledge Of Things Familiar Part 31

"Mackarels' scales and mares' tails Make lofty s.h.i.+ps to carry low sails."

Q. _How are COMPOUND CLOUDS sub-divided?_

A. Compound clouds are also sub-divided into two sorts. 1.--The c.u.m'ulo-stra'tus; and 2.--The Nimbus.

Q. _What is meant by c.u.m'ULO-STRA'TUS clouds?_

A. Those clouds which a.s.sume all sorts of _gigantic fancy forms_; such as vast towers and rocks,--huge whales and dragons,--scenes of battle,--and cloudy giants. This cla.s.s of clouds is the most romantic and strange of all.

Q. _What do the c.u.mulo-stratus clouds foretell?_

A. _A change of weather_; either from fine to rain, or from rain to fine weather.

Q. _What are NIMBUS CLOUDS?_

A. Nimbus is the Latin word for "clouds which bring a storm;" and all clouds from which _rain falls_ are so named.

Q. _What APPEARANCE takes place in the CLOUDS at the approach of RAIN?_

A. The _c.u.m'ulus_ cloud becomes _stationary_, and _cirrus streaks settle upon it_, forming c.u.mulo-stratus clouds; which are _black_ at first, but afterwards of a _grey_ colour.

Q. _Why do CLOUDS gather ROUND MOUNTAIN-TOPS?_

A. Because (as they float along) _they dash against the mountains_; and (being _arrested_ in their motion) collect round the top.

Q. _What is the USE of CLOUDS?_

A. 1st--They act as screens to arrest _the radiation of heat from the earth_:

2ndly--They temper the heat of the _sun's rays_: and

3rdly--They are the great _store-houses of rain_.

Q. _Why is WIND said to BLOW UP the CLOUDS?_

A. When a _dry_ wind travels over sea, and acc.u.mulates _more_ vapour than the air can _sustain_, it _relinquishes a part_ (as it flies along) in the form of clouds.

Q. _Why does WIND sometimes DRIVE AWAY the CLOUDS?_

A. When wind travels over _dry climes_ or _thirsty deserts_, it becomes _so dry itself_, that it absorbs vapour from the clouds, and _disperses_ them.

Q. _What is the CAUSE of a RED SUN-SET?_

A. Because the vapour of the air is not _actually condensed into clouds_, but only on the _point of being condensed_; in which state it bends the _red rays of the sun towards the horizon_, where they are reflected at sun-set.

Q. _Why is a RED SUN-SET an indication of a FINE DAY to-morrow?_

A. Because (notwithstanding the cold of sun-set) the vapours of the earth are _not condensed into clouds_. Our Lord referred to this prognostic in the following words: "When it is evening ye say, it will be fair weather, for the sky is red." (Matt. xvi. 2.)

Q. _What is the cause of a coppery YELLOW SUN-SET?_

A. Because the vapour of the air is _actually condensed into clouds_; in which case it "refracts" (or bends) the _yellow rays of the sun towards the horizon_, where they are reflected at sun-set.

Q. _Why is a YELLOW SUNSET an indication of WET?_

A. Because the vapours of the air _are already condensed into clouds_; rain, therefore, may be shortly expected.

Q. _What is the cause of a RED SUN-RISE?_

A. Vapour in the upper region of the air _just on the point of being condensed_.

Q. _Why is a RED and LOWERING sky at SUNRISE an indication of a WET DAY?_

A. Because the higher regions of the air are _laden with vapour_, on the very _point of condensation_, which the rising sun cannot disperse.

Hence our Lord's observation, "In the morning (ye say) it will be foul weather to-day, for the sky is red and lowering." (Matt. xvi. 3.)

Q. _Why is a GREY MORNING an indication of a FINE DAY?_

A. Because _that_ air alone _contiguous to the earth_ is damp and full of vapour. There are no vapours in the _higher_ regions of the air _to reflect red rays_; and hence the morning-light looks grey.

Q. _What difference (in the state of the air) is required, to make a GREY and RED SUNRISE?_

A. In a _grey_ sunrise, only that portion of air _contiguous to the earth is filled with vapour_; all the rest is clear and dry. But in a _red_ sunrise the air in the _upper regions_ is so full of vapour that the rising sun cannot disperse it.

Q. _Why is a GREY SUNSET an indication of WET?_

A. If the air on the _surface of the earth_ be very _damp at sunset_, it is a proof that the air is _saturated with vapour_, and wet may be expected: hence the proverb--

"Evening red and morning grey Will set the traveller on his way; But evening grey and morning red Will bring down rain upon his head."