Part 89 (2/2)
Q. _Why are potatoes (which grow EXPOSED to the air and light) GREEN?_
A. Because the sun-light _increases their carbon_; which (mingling with the yellow sap) turns the potato _green_.
Q. _Why is it DANGEROUS to SLEEP in a room which contains LIVING PLANTS?_
A. Because they _exhale carbon in the dark_ in the form of CARBONIC ACID GAS, which is destructive to animal life.
Q. _Why are SOME things (like gla.s.s) TRANSPARENT?_
A. In transparent bodies (like gla.s.s) all the rays of light _emerge on the opposite side_.
Q. _Why are SOME things s.h.i.+NING and splendid?_
A. Those objects which _reflect the most rays_ are the most _splendid_; and those which _absorb_ them most, are _dull_.
Q. _Why are DESERTS so DAZZLING in summer time?_
A. Because each separate grain of sand _reflects the rays of the sun_ like a mirror.
Q. _If you move a stick (burnt at one end) ROUND pretty briskly, it seems to make a CIRCLE OF FIRE,--WHY is this?_
A. Because the eye _retains the image_ of any bright object, _after the object itself is withdrawn_; and as the spark of the stick returns _before the image has faded_ from the eye, therefore, it seems to form a _complete circle_.
Q. _If separate figures (as a man and a horse) be drawn on separate sides of a card, and the card TWISTED quickly, the man seems to be seated on the horse,--WHY is this?_
A. Because the image of the horse _remains upon the eye_ till the _man_ appears.
The Thaumatrope is constructed on this principle.
Q. _Why do the STARS TWINKLE?_
A. Fixed stars are _so far off_, that their rays of light do not strike upon the eye _in a continuous flow_, but at _intervals_: when their rays _reach the eye_, the star becomes _visible_, and then is obscured _till the next batch of rays arrive_; and this _perpetually_ occurring, makes a kind of _twinkling_.
Q. _If we look at a RED-hot FIRE for a few minutes, WHY does every thing seem TINGED with a BLUISH GREEN colour?_
A. Because bluish green is the ”ACCIDENTAL COLOUR” of red: and if we fix our eye upon _any colour whatsoever_, when we turn aside, we see every object tinged with _its accidental colour_.
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