A Guide To The Scientific Knowledge Of Things Familiar Part 75

A. 1st--Because the _air is more highly electrified_ in summer and autumn: and

2ndly--The vapours (being rarefied) ascend to the more elevated regions, where the _cold is greater_ than it is nearer the earth.

Q. _What TWO things are essential to cause HAIL?_

A. Two _strata of clouds_ having _opposite electricities_, and _two currents of wind_. The _lower cloud_ (being negative) is the one _precipitated_.

Q. _What is RAIN?_

A. The vapour of the clouds or air _condensed_, and precipitated to the earth.

Q. _Why is the vapour of the air or clouds PRECIPITATED?_

A. When the air is _saturated with vapour_, if a cold current _condenses_ it, it is no longer _able to hold all its vapour_ in solution, and some of it is squeezed out, and falls as rain.

Q. _Why does RAIN fall in DROPS?_

A. The vapoury particles in their descent _attract each other_; and those which are sufficiently near, _unite_ and form into a drop.

Q. _Why does not the COLD of NIGHT ALWAYS cause rain?_

A. When the air is not _near saturation_ (although condensed by the chill of evening), it will still be able to hold its vapour in solution.

Q. _Why does a Pa.s.sING CLOUD often drop RAIN?_

A. Because the cloud (travelling about on the wind) comes into contact with _something that chills it_; and its vapour being squeezed out, _falls to the earth as rain_.

Q. _Why are RAIN-DROPS sometimes much LARGER than at OTHER times?_

A. When the rain-cloud is floating _near the earth_, the drops are large, because such a cloud is _much more dense_ than one which is more elevated.

The size of the rain-drop is increased according to the _rapidity_ with which the vapours are condensed.

Q. _Does not WIND sometimes INCREASE the SIZE of rain-drops?_

A. Yes; by blowing two or more drops into one.

Q. _Why do CLOUDS FALL in RAINY weather?_

A. 1st--Because the _clouds are heavy_ with abundant vapour: and

2ndly--As the density of the air is _diminished_, it is less able to buoy the clouds up.

Q. _How do you KNOW that the DENSITY of the air is DIMINISHED in RAINY weather?_

A. Because the _mercury of a barometer falls_.

Q. _Why is RAIN-water more FERTILIZING than PUMP-water?_

A. Because it contains a compound of hydrogen and nitrogen (called _ammonia_), which is a very excellent food for young plants.

Q. _Why is NOVEMBER made by G.o.d to be a RAINY MONTH?_

A. Because rain _hastens the putrefaction of the fallen leaves_ by causing fermentation.

Q. _Why does RAIN PURIFY the AIR?_

A. 1st--Because it _beats down the noxious exhalations_ collected in the air, and _dissolves_ them:

2ndly--It mixes the air of the _upper_ regions with that of the _lower regions_: and

3rdly--It _washes the earth_, and sets in motion the stagnant _sewers and ditches_.

Q. _Why are MOUNTAINOUS countries more RAINY than flat ones?_

A. The air (striking against the side of the mountains) is _carried up the inclined plane_, and brought in contact with the _cold air of the higher regions_, by which it is _condensed_, and its _vapour squeezed out_.

Q. _Why does a SPONGE SWELL when it is WETTED?_

A. Because the water _penetrates the pores_ of the sponge, and drives the particles of the sponge _further from each other_; in consequence of which, the _bulk_ of the sponge is greatly _increased_.

Q. _Why do FIDDLE-strings SNAP in WET weather?_

A. Because the moisture of the air (penetrating the string) _causes it to swell_; and (as the cord _thickens_) its _tension is increased_, and the string snaps.

Q. _Why does PAPER PUCKER when it is WETTED?_

A. Because the moisture (penetrating the paper) _drives its particles further apart_; and (as the moisture is absorbed _unequally_ by the paper) some parts are more enlarged than others; in consequence of which, the paper _blisters_ or _puckers_.

Q. _Why do the weather toys called CAPU'CHINS lift the cowl over the figures in wet weather, and remove it in dry?_