A Guide To The Scientific Knowledge Of Things Familiar Part 29

Q. _Are ALL clouds ALIKE?_

A. No. They vary greatly in _density, height, and colour_.

Q. _What is the chief CAUSE of fog and CLOUDS?_

A. The changes of the wind.

Q. _How can the CHANGES of the WIND affect the CLOUDS?_

A. If a _cold current of wind_ blows suddenly over any region, it _condenses_ the invisible vapour of the air into _cloud or rain_: but if a _warm current of wind_, blows over any region, it _disperses_ the clouds, by _absorbing their vapour_.

Q. _What_ COUNTRIES _are the_ MOST CLOUDY?

A. Those where the winds are _most variable_, as Britain.

Q. _What COUNTRIES are the LEAST cloudy?_

A. Those where the winds are _not variable_, as Egypt.

Q. _What DISTANCE are the CLOUDS from the EARTH?_

A. Some _thin light clouds_ are elevated above the highest mountain-top; some _heavy_ ones touch the steeples, trees, and even the earth: but the _average_ height is between _one and two miles_.

(Streaky curling clouds, _like hair_, are often five or six miles high.)

Q. _What CLOUDS are the LOWEST?_

A. Those that are _most highly electrified_: lightning clouds are rarely more than about 700 yards above the ground; and very often actually _touch the earth with one of their edges_.

Q. _What is the THICKNESS of the CLOUDS?_

A. Some clouds are 20 _square miles in surface_, and above _a mile in thickness_; while others are only a _few yards or inches_.

Q. _How can persons ascertain the thickness of a cloud?_

A. As the _tops of high mountains_ are generally _above the clouds_; therefore, travellers (who climb the mountains) may _pa.s.s quite through the clouds_, into a clear blue firmament, when they may see the clouds _beneath their feet_.

Q. _Why are the CLOUDS so VARIABLE in SHAPE?_

A. The _shape_ of clouds depends upon two things:--Their state of _electricity_, and _the wind_.

Q. _How can ELECTRICITY affect the SHAPE of CLOUDS?_

A. If one cloud be _full of electricity_, and another _not_, they will be _attracted to each other_, and either coalesce,--diminish in size,--or vanish altogether.

Q. _Which clouds a.s.sume the most FANTASTIC shapes?_

A. Those that are the most _highly electrified_.

Q. _What effect have WINDS on the SHAPE of CLOUDS?_

A. They sometimes _absorb them entirely_: sometimes _increase their volume and density_; and sometimes _change the position of their parts_.

Q. _How can WINDS ABSORB CLOUDS altogether?_

A. _A warm dry wind_ will convert the substance of the clouds into _invisible vapour_, and carry it in its own current.

Q. _How can WINDS INCREASE the bulk and density of CLOUDS?_

A. A _cold_ current of wind will _condense the invisible vapour of the air_, and _add it to the clouds_ as it pa.s.ses by.

Q. _How can WINDS CHANGE the SHAPE of CLOUDS by altering the position of their parts?_

A. Because clouds are so voluble and light, that every breath of wind changes the position of those ves'cicles or bubbles.

Q. _What are the general COLOURS of the CLOUDS?_

A. White and grey, _when the sun is above the horizon_: but red, orange, and yellow, _at sun-rise and sun-set_.

The _blue sky_ cannot be considered as _clouds_ at all.

Q. _Why are the LAST CLOUDS of EVENING generally of a RED tinge?_

A. Because _red_ rays are the _least refrangible of all_; and, therefore, _are the last to disappear_.

Q. _What is meant by being "LESS REFRANGIBLE"?_

A. Being _less able to be bent_. Blue and green rays being very easily bent (_by the resistance of the air_) are thrown _off from the horizon_; but red rays not being _bent back_ in the same way, give a tinge to the evening clouds.