按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
before the point H has risen far。
6
Mock suns； and rods too； are due to the causes we have described。
A mock sun is caused by the reflection of sight to the sun。 Rods are
seen when sight reaches the sun under circumstances like those which
we described； when there are clouds near the sun and sight is
reflected from some liquid surface to the cloud。 Here the clouds
themselves are colourless when you look at them directly； but in the
water they are full of rods。 The only difference is that in this
latter case the colour of the cloud seems to reside in the water；
but in the case of rods on the cloud itself。 Rods appear when the
composition of the cloud is uneven； dense in part and in part rare；
and more and less watery in different parts。 Then the sight is
reflected to the sun： the mirrors are too small for the shape of the
sun to appear； but； the bright white light of the sun； to which the
sight is reflected； being seen on the uneven mirror； its colour
appears partly red； partly green or yellow。 It makes no difference
whether sight passes through or is reflected from a medium of that
kind； the colour is the same in both cases； if it is red in the
first case it must be the same in the other。
Rods then are occasioned by the unevenness of the mirror…as
regards colour； not form。 The mock sun； on the contrary； appears
when the air is very uniform； and of the same density throughout。 This
is why it is white： the uniform character of the mirror gives the
reflection in it a single colour； while the fact that the sight is
reflected in a body and is thrown on the sun all together by the mist；
which is dense and watery though not yet quite water； causes the sun's
true colour to appear just as it does when the reflection is from
the dense； smooth surface of copper。 So the sun's colour being
white； the mock sun is white too。 This； too； is the reason why the
mock sun is a surer sign of rain than the rods； it indicates； more
than they do； that the air is ripe for the production of water。
Further a mock sun to the south is a surer sign of rain than one to
the north； for the air in the south is readier to turn into water than
that in the north。
Mock suns and rods are found； as we stated； about sunset and
sunrise； not above the sun nor below it； but beside it。 They are not
found very close to the sun； nor very far from it； for the sun
dissolves the cloud if it is near； but if it is far off the reflection
cannot take place； since sight weakens when it is reflected from a
small mirror to a very distant object。 （This is why a halo is never
found opposite to the sun。） If the cloud is above the sun and close to
it the sun will dissolve it； if it is above the sun but at a
distance the sight is too weak for the reflection to take place； and
so it will not reach the sun。 But at the side of the sun； it is
possible for the mirror to be at such an interval that the sun does
not dissolve the cloud； and yet sight reaches it undiminished
because it moves close to the earth and is not dissipated in the
immensity of space。 It cannot subsist below the sun because close to
the earth the sun's rays would dissolve it； but if it were high up and
the sun in the middle of the heavens； sight would be dissipated。
Indeed； even by the side of the sun； it is not found when the sun is
in the middle of the sky； for then the line of vision is not close
to the earth； and so but little sight reaches the mirror and the
reflection from it is altogether feeble。
Some account has now been given of the effects of the secretion
above the surface of the earth； we must go on to describe its
operations below； when it is shut up in the parts of the earth。
Just as its twofold nature gives rise to various effects in the
upper region； so here it causes two varieties of bodies。 We maintain
that there are two exhalations； one vaporous the other smoky； and
there correspond two kinds of bodies that originate in the earth；
'fossiles' and metals。 The heat of the dry exhalation is the cause
of all 'fossiles'。 Such are the kinds of stones that cannot be melted；
and realgar； and ochre； and ruddle； and sulphur； and the other
things of that kind； most 'fossiles' being either coloured lye or；
like cinnabar； a stone compounded of it。 The vaporous exhalation is
the cause of all metals； those bodies which are either fusible or
malleable such as iron； copper； gold。 All these originate from the
imprisonment of the vaporous exhalation in the earth； and especially
in stones。 Their dryness compresses it； and it congeals just as dew or
hoar…frost does when it has been separated off； though in the
present case the metals are generated before that segregation
occurs。 Hence； they are water in a sense； and in a sense not。 Their
matter was that which might have become water； but it can no longer do
so： nor are they； like savours； due to a qualitative change in
actual water。 Copper and gold are not formed like that； but in every
case the evaporation congealed before water was formed。 Hence； they
all （except gold） are affected by fire； and they possess an
admixture of earth； for they still contain the dry exhalation。
This is the general theory of all these bodies； but we must take
up each kind of them and discuss it separately。
Book IV
1
WE have explained that the qualities that constitute the elements
are four； and that their combinations determine the number of the
elements to be four。
Two of the qualities； the hot and the cold； are active； two； the dry
and the moist； passive。 We can satisfy ourselves of this by looking at
instances。 In every case heat and cold determine； conjoin； and
change things of the same kind and things of different kinds；
moistening； drying； hardening； and softening them。 Things dry and
moist； on the other hand； both in isolation and when present
together in the same body are the subjects of that determination and
of the other affections enumerated。 The account we give of the
qualities when we define their character shows this too。 Hot and
cold we describe as active； for 'congregating' is essentially a
species of 'being active'： moist and dry are passive； for it is in
virtue of its being acted upon in a certain way that a thing is said
to be 'easy to determine' or 'difficult to determine'。 So it is
clear that some of the qualities are active and some passive。
Next we must describe the operations of the active qualities and the
forms taken by the passive。 First of all； true becoming； that is；
natural change； is always the work of these powers and so is the
corresponding natural destruction； and this becoming and this
destruction are found in plan