A Guide To The Scientific Knowledge Of Things Familiar Part 74

CHAPTER XXIV.

SNOW. HAIL. RAIN.

Q. _What is SNOW?_

A. The condensed vapour of the air _frozen_, and precipitated to the earth.

Q. _What is the CAUSE of SNOW?_

A. When the air is nearly saturated with vapour, and condensed by a current of air _below freezing point_, some of the vapour is squeezed out, and frozen into snow.

A few years ago, some fishermen (who wintered at Nova-Zembla), after they had been shut up in a hut for several days, _opened the window_, and the cold external air rushing in, instantly condensed the air of the hut, and the vapour (which was squeezed out) fell on the floor _in a shower of snow_.

Q. _Why does SNOW fall in WINTER time?_

A. Because the sun's rays are too _oblique_ to heat the surface of the earth; and (as the _earth has no heat_ to radiate into the air) the air is very cold.

Q. _What is SLEET?_

A. When flakes of snow (in their descent) pa.s.s through a bed of air _above freezing point_, they melt; and fall to the earth as half-melted snow or sleet.

Q. _What is the USE of SNOW?_

A. To keep the _earth warm_, and to _nourish_ it.

Q. _How can snow keep the EARTH WARM?_

A. Because it is a very _bad conductor_; in consequence of which, the earth which is covered with snow, very rarely descends _below freezing point_, even when the air is 15 or 20 degrees colder.

Q. _Why is SNOW a BAD CONDUCTOR of heat and cold?_

A. Because _air_ is confined and entangled between the crystals, and _air_ is a very _bad conductor_; when, therefore, the earth is covered with snow, it cannot throw off its heat by radiation.

Q. _Tell me the words of the PSALMIST_ (cxlvii. 16.) _respecting snow, and explain what he means._

A. The Psalmist says--"The Lord giveth snow like wool:" and he means not only that snow is as _white as wool_, but that it is also as _warm as wool_.

Q. _Why is WOOL WARM?_

A. Because _air_ is entangled between the fibres of the wool, and air is a _bad conductor_.

Q. _Why is SNOW WARM?_

A. Because _air_ is entangled between the crystals of the snow, and air is a _bad conductor_.

Q. _Why does SNOW NOURISH the earth?_

A. Because it supplies it with _moisture_ for a considerable time; which penetrates slowly into the soil, and insinuates itself through every clod, ridge, and furrow.

Q. _Why is there NO SNOW in SUMMER time?_

A. No snow reaches the general surface of the earth in summer time, because the _heat of the earth_ melts it in its descent.

Q. _Why are some MOUNTAINS ALWAYS COVERED with SNOW?_

A. 1st--Because the _air is more rarefied_; and rarefied air _abstracts heat_ which it holds in a _latent state_:

2ndly--As the mountain top is _not surrounded by earth_ to radiate heat into the air; therefore, the snow is _not melted_ in its descent, but falls on the mountain, and lies there.

Q. _Why is SNOW WHITE?_

A. Snow is formed of an infinite number of very minute crystals and prisms, which reflect all the colours of the rays of light; and these colours _uniting_ before they meet the eye, cause snow to appear white.

Q. _What is HAIL?_

A. Rain, which has pa.s.sed in its descent _through some cold bed of air_, and has been frozen into drops of ice.

Q. _Why is ONE bed of air COLDER than another?_

A. This is frequently caused by _electricity_ in the air, _unequally distributed_.

Q. _Why is HAIL frequently accompanied with THUNDER and LIGHTNING?_

A. 1st--Because the _congelation of water into hail_ disturbs the electricity of the air: and

2ndly--The _friction_ (produced by the fall of hail) excites it still more.

Q. _Why does HAIL fall generally in SUMMER and AUTUMN?_