The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million — John Stuart Mill — John Shaqi
The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
John Stuart Mill · en
844. _Why does the flying-top return to the earth when its rotations
are expended?_
Because the _reaction_ produced by its wings striking upon the air, is
insufficient to counteract the _attraction of gravitation_.
[Illustration: Fig. 34.--FLYING-TOP.]
[Illustration: Fig. 35.--PEA AND PIPE.]
845. _Why does a pea, into which a pin has been stuck, dance in
suspension upon a jet of air blown through a pipe?_
Because the jet of air, being _slightly compressed_ under the _convex_
form of the pea, by the weight of the pin, forms a _concave cup of
air_, in which the pea rests.
In the case put, it is supposed that the pin is _passed through
the pea_ until its head comes in contact with it. The pin is
dropped into the hole of the pipe, and the breath is then applied,
the pipe being held upright. The pea will rise in the air, and be
suspended upon the jet, while the point of the pin will rotate
around the stem of the pipe. There are other methods of fixing the
pin which alter the result, and require a different explanation to
that given above.
LESSON XL.
846. _Why does a mouse, painted upon one side of a card, and a trap
upon the other, represent to the eye a mouse in a trap when the card
is rapidly twirled upon a string?_
Because the image of the mouse is brought to the retina of the eye
before the image of the trap has passed away. The two impressions,
therefore, _unite upon the retina_, and produce the image of a mouse in
a trap.
[Verse: "Honour thy father and thy mother * * That it may be well
with thee, and thou mayest be long on the earth."--EPHESIANS VI.]
[Illustration: Fig. 36.--CARD WITH MOUSE-TRAP.]
[Illustration: Fig. 37.--REVERSE OF CARD WITH MOUSE.]
847. _Why will a bow stretched out of its natural position, propel an
arrow through the air?_
Because its substance, being _highly elastic_, the particles thereof
seek to restore themselves to their former state, as soon as the
resisting power is withdrawn. The _force_ derived from this elasticity,
is communicated to the arrow by the string against which it is placed.
848. _Why is the arrow propelled forward?_
Because the elasticity of the bow, _acting equally upon its two ends_,
to which the string is fastened, produce a line of force in a _diagonal
direction_. It thus illustrates the law, that _when a body is acted
upon by two forces at the same time, whose directions are inclined to
each other, it will not follow either of them, but will describe a line
between the two_.
849. _What forces tend to arrest the flight of the arrow?_
The _friction of the air_, and the _attraction of gravitation_.
[Verse: "My son, give, I pray thee, glory to the Lord God of Israel,
and make confession unto him."--JOSHUA VII.]
850. _Why are feathers usually fastened to the ends of arrows?_