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
This is one of the most striking instances that can be afforded
of the wonderful properties of light, and of the infinitude of
those luminous rays that attend the majestic rising of the sun.
Not only does light fly from the grand "ruler of the day" with
a velocity which is a million and a half times greater than
the speed of a cannon-ball, but it darts from every reflecting
surface with a like velocity, and reaches the tender structure of
the eye so gently that, as it falls upon the little curtain of
nerves which is there spread to receive it, it imparts the most
pleasing sensations, and tells its story of the outer world with a
minuteness of detail, and a holiness of truth. Philosophers once
sought to _weigh_ the _sunbeam_; they constructed a most delicate
balance, and suddenly let in upon it a beam of light; the lever
of the balance was so delicately hung that the fluttering of a
fly would have disturbed it. Everything prepared, the grave men
took their places, and with keen eyes watched the result. The
sunbeam that was to decide the experiment had left the sun eight
minutes prior to pass the ordeal. It had flown through ninety-five
millions of miles of space in that short measure of time, and it
shot upon the balance with unabated velocity: but the lever moved
not, and the philosophers were mute.
CHAPTER XXV.
518. _Why, when we move before a mirror, does the image draw near
to the reflecting surface as we draw near to it, and retire when we
retire?_
Because the lines and angles of _reflection_ are always equal to the
lines and angles of _incidence_.
519. _What is the line of incidence?_
If a person stands in a direct line before a mirror, the line through
which the light travels from him to the mirror is _the line of
incidence_.
_Incidence_--falling on.
[Verse: "Blessed be the Lord, who daily loadeth us with benefits,
even the God of our salvation."--PSALM LXVIII.]
520. _What is the line of reflection?_
The _line of reflection_ is the line in which the rays of light are
returned from the image formed in the glass to the eye of the observer.
_Reflection_--a turning back.
521. _What is the angle of incidence?_
The _angle_ of incidence is the angle which rays of light, falling on a
reflecting surface, make with a line perpendicular to that surface.
[Illustration: Fig. 14.--EXPLAINING THE LINES AND ANGLES OF INCIDENCE
AND OF REFLECTION.]
522. _What is the angle of reflection?_
The _angle_ of reflection is the angle which is formed by the returning
rays of light, and a line perpendicular to the reflecting surface. It
is always _equivalent_ to the angle of incidence.