A Guide To The Scientific Knowledge Of Things Familiar Part 88

[Ill.u.s.tration: Here it will be seen that the red ray PA, being reflected on the horizon at A, will be visible to us; but the YELLOW and BLUE rays will be hidden by the curve of the earth.]

Q. _Why are the early MORNING clouds RED?_

A. Because RED rays (being the _least refrangible_) are the _first to appear_.

_See last figure._--It is evident that PA (the red rays) will be reflected on the horizon before either the yellow or blue ones.

Q. _What becomes of the BLUE and YELLOW rays?_

A. They are refracted _below the horizon_, and are soon made invisible by the _curve of the earth_. (_See last figure._)

Q. _Why are the EDGES of CLOUDS more LUMINOUS than their CENTRES?_

A. Because the _body of vapour is thinnest_ at the edges of the clouds.

Q. _What is the cause of morning and evening TWILIGHT?_

A. When the sun is below the horizon, the rays (which strike upon the atmosphere or clouds) _are bent down towards the earth_, and produce a little light called twilight.

_See figure on p. 399._--Here the rays of PA will give _some_ light.

Q. _Why is a ray of LIGHT composed of VARIOUS COLOURS?_

A. If solar light were of _one colour only_, all objects would appear of _that one colour_ (or else black.)

Q. _Why are some things of ONE COLOUR, and some of ANOTHER?_

A. As every ray of light is composed of all the colours of the rainbow, _some_ things reflect _one of these colours_, and some _another_.

Q. _Why do some things reflect ONE COLOUR, and some ANOTHER?_

A. Because the _surface_ of things is so _differently constructed_, both physically and chemically; and, therefore, _some_ things reflect _one_ ray; some _two rays_; some _all_ the rays; and some _none_.

Q. _What mainly determines the COLOUR of any object?_

A. The fluid or gas either _in_ the body, or on its _surface_.

N. B. Nitrogen gives green,--Oxygen gives red,--Hydrogen gives blue colours.

Q. _Why does DYING a silk, &c. CHANGE its COLOUR?_

A. Because the materials used in dyeing _alter the chemical construction_ of the substance dyed.

Q. _Why is a ROSE RED?_

A. Because the surface of a rose _absorbs the blue and yellow_ rays of light, and _reflects_ only the _red_ ones.

Q. _Why does a rose absorb the yellow and blue rays, and reflect the RED?_

A. Because the action of the sun's rays on the oxygen (acc.u.mulated in the petals) produces an _acid_ which turns them _red_.

The leaves which compose a flower, are called PETALS.

Q. _Why is a VIOLET BLUE?_

A. Because the surface of the violet _absorbs the red and yellow_ rays of the sun, and _reflects_ the _blue_ only.

Q. _Why do violets absorb the red and yellow rays, and reflect the BLUE?_

A. Because the petals of the violet contain an _alkali_, which gives them a _purple tinge_.

Q. _Why is a PRIMROSE YELLOW?_

A. Because the surface of the primrose _absorbs the blue and red_ rays of solar light, and _reflects_ the _yellow_ ones.

All plants which have much alkali in their ash, have blue or yellow flowers.

Those which have acid in their ash, have orange, pink, or red flowers.

N. B. Anti-acids (like soda) are called ALKALIS.

Q. _Why are some things BLACK?_

A. Because they _absorb all the rays of light_, and reflect _none_.

Q. _Why are some things WHITE?_