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
[Verse: "A man that is called Jesus made clay, and anointed mine
eyes, and said unto me, Go to the pool of Siloam, and wash: and I went
and washed, and I received sight."--JOHN IX.]
551. _Why are two persons able to see each other?_
Because rays of light _flow from their bodies to each other's eyes_,
and convey an impression of their respective conditions.
In some popular works that have come under our notice, we find
that the student is told that "we cannot absolutely see each
other--we only _see the rays of light reflected from each other_."
The statement is erroneous as expressed. We do not see the
_rays_ of light, for if we did so, the effect of vision would
be destroyed, and all bodies would _appear_ to be in a state of
_incandesence_, or of _phosphoresence_. Rays of light, which are
in themselves _invisible_, radiate from the objects we look upon,
enter the pupil of the eye, and impress the seat of vision in a
manner which conveys to the mind a knowledge of the form, colour,
and relative size and position of the figure we look upon. If
this is not seeing the object--_what is_? It would be just as
reasonable to say, that we cannot _hear_ a person speak--that we
only hear the _vibrations of the air_. But as the vibrations are
imparted to the air by the organs of voice of the speaker, as he
sets the air in motion, and makes the air his messenger to us, we
certainly hear _him_, and can dispense with any logical myths that
confound the understanding, and contribute to no good result.
552. _What is actinism?_
_Actinism_ is the chemical property of light.
_Actinism_--ray power.
553. _Why does silver tarnish when exposed to light?_
Because of the _actinic_, or chemical power of the rays of the sun.
554. _Why do some colours fade, and others darken, when exposed to the
sun?_
Because of the _chemical_ power of the sun's rays.
555. _Why can pictures be taken by the sun's rays?_
Because of the actinic powers that accompany the solar light.
556. _What is the particular chemical effect of light exhibited in the
production of photographic pictures?_
Simply the _darkening of preparations of silver, by the actinic rays_.
557. _Why are photographic studios usually glazed with blue glass?_
Because blue glass obstructs many of the luminous rays, but it is
perfectly transparent to _actinism_.
[Verse: "The hay appeareth, and the tender grass showeth itself, and
herbs of the mountain are gathered."--PROV. XXVII.]
558. _Why do plants become scorched under the unclouded sun?_
Because the heat rays are in excess. The clouds shut off the scorching
light; but, like the blue glass of the photographer's studio, they
transmit _actinism_.
559. _What effect has actinism upon vegetation?_