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Epicurus to Pythocles, greetings:
In your letter to me, of which Cleon was
the bearer, you continue to show me affection
which I have merited by my devotion to you,
and you try, not without success, to recall
the considerations which make for a happy
life. To aid your memory you ask me for a
clear and concise statement respecting celestial
phenomena; for what we have written on this
subject elsewhere is, you tell me, hard to
remember, although you have my books constantly
with you. I was glad to receive your request
and am full of pleasant expectations. We
will then complete our writing and grant
all you ask. Many others besides you will
find these reasonings useful, and especially
those who have but recently made acquaintance
with the true story of nature and those who
are attached to pursuits which go deeper
than any part of ordinary education. So you
will do well to take and learn them and get
them up quickly along with the short epitome
in my letter to Herodotus.
In the first place, remember that, like everything
else, knowledge of celestial phenomena, whether
taken along with other things or in isolation,
has no other end in view than peace of mind
and firm convictions. We do not seek to wrest
by force what is impossible, nor to understand
all matters equally well, nor make our treatment
always as clear as when we discuss human
life or explain the principles of physics
in general-for instance, that the whole of
being consists of bodies and intangible nature,
or that the ultimate elements of things are
indivisible, or any other proposition which
admits only one explanation of the phenomena
to be possible. But this is not the case
with celestial phenomena: these at any rate
admit of manifold causes for their occurrence
and manifold accounts, none of them contradictory
of sensation, of their nature.
For in the study of nature we must not conform
to empty assumptions and arbitrary laws,
but follow the promptings of the facts; for
our life has no need now of unreason and
false opinion; our one need is untroubled
existence. All things go on uninterruptedly,
if all be explained by the method of plurality
of causes in conformity with the facts, so
soon as we duly understand what may be plausibly
alleged respecting them. But when we pick
and choose among them, rejecting one equally
consistent with the phenomena, we clearly
fall away from the study of nature altogether
and tumble into myth. Some phenomena within
our experience afford evidence by which we
may interpret what goes on in the heavens.
We see bow the former really take place,
but not how the celestial phenomena take
place, for their occurrence may possibly
be due to a variety of causes. However, we
must observe each fact as presented, and
further separate from it all the facts presented
along with it, the occurrence of which from
various causes is not contradicted by facts
within our experience.
A world is a circumscribed portion of the
universe, which contains stars and earth
and all other visible things, cut off from
the infinite, and terminating in an exterior
which may either revolve or be at rest, and
be round or triangular or of any other shape
whatever. All these alternatives are possible:
they are contradicted by none of the facts
in this world, in which an extremity can
nowhere be discerned.
That there is an infinite number of such
worlds can be perceived, and that such a
world may arise in a world or in one of the
intermundia (by which term we mean the spaces
between worlds) in a tolerably empty space
and not. as some maintain, in a vast space
perfectly clear and void. It arises when
certain suitable seeds rush in from a single
world or intermundium, or from several, and
undergo gradual additions or articulations
or changes of place, it may be, and waterings
from appropriate sources, until they are
matured and firmly settled in so far as the
foundations laid can receive them. For it
is not enough that there should be an aggregation
or a vortex in the empty space in which a
world may arise, as the necessitarians hold,
and may grow until it collide with another,
as one of the so-called physicists says.
For this is in conflict with facts.
The sun and moon and the stars generally
were not of independent origin and later
absorbed, within our world, [such parts of
it at least as serve at all for its defense];
but they at once began to take form and grow
[and so too did earth and sea] by the accretions
and whirling motions of certain substances
of finest texture, of the nature either of
wind or fire, or of both; for thus sense
itself suggests.
The size of the sun and the remaining stars
relatively to us is just as great as it appears.
But in itself and actually it maybe a little
larger or a little smaller, or precisely
as great as it is seen to be. For so too
fires of which we have experience are seen
by sense when we see them at a distance.
And every objection brought against this
part of the theory will easily be met by
anyone who attends to plain facts, as I show
in my work On Nature. And the rising and
setting of the sun, moon, and stars may be
due to kindling and quenching, a provided
that the circumstances are such as to produce
this result in each of the two regions, east
and west: for no fact testifies against this.
Or the result might be produced by their
coming forward above the earth and again
by its intervention to hide them: for no
fact testifies against this either. And their
motions may be due to the rotation of the
whole heaven, or the heaven may be at rest
and they alone rotate according to some necessary
impulse to rise, implanted at first when
the world was made . . . and this through
excessive heat, due to a certain extension
of the fire which always encroaches upon
that which is near it.
The turnings of the sun and moon in their
course may be due to the obliquity of the
heaven, whereby it is forced back at these
times. Again, they may equally be due to
the contrary pressure of the air or, it may
be, to the fact that either the fuel from
time to time necessary has been consumed
in the vicinity or there is a dearth of it.
Or even because such a whirling motion was
from the first inherent in these stars so
that they move in a sort of spiral. For all
such explanations and the like do Dot conflict
with any clear evidence, if only in such
details we hold fast to what is possible,
and can bring each of these explanations
into accord with the facts, unmoved by the
servile artifices of the astronomers.
The waning of the moon and again her waxing
a might be due to the rotation of the moon's
body, and equally well to configurations
which the air assumes; further, it may be
due to the interposition of certain bodies.
In short, it may happen in any of the ways
in which the facts within our experience
suggest such an appearance to be explicable.
But one must not be so much in love with
the explanation by a single way as wrongly
to reject all the others from ignorance of
what can, and what cannot, be within human
knowledge, and consequent longing to discover
the undiscoverable. Further, the moon may
possibly shine by her own light, just as
possibly she may derive her light from the
sun; for in our own experience we see many
things which shine by their own light and
many also which shine by borrowed light.
And none of the celestial phenomena stand
in the way, if only we always keep in mind
the method of plural explanation and the
several consistent assumptions and causes,
instead of dwelling on what is inconsistent
and giving it a false importance so as always
to fall back in one way or another upon the
single explanation. The appearance of the
face in the moon may equally well arise from
interchange of parts, or from interposition
of something, or in any other of the ways
which might be seen to accord with the facts.
For in all the celestial phenomena such a
line of research is not to be abandoned;
for, if you fight against clear evidence,
you never can enjoy genuine peace of mind.
An eclipse of the sun or moon may be due
to the extinction of their light, just as
within our own experience this is observed
to happen; and again by interposition of
something else - whether it be the earth
or some other invisible body like it. And
thus we must take in conjunction the explanations
which agree with one another, and remember
that the concurrence of more than one at
the same time may not impossibly happen.
And further, let the regularity of their
orbits be explained in the same way as certain
ordinary incidents within our own experience;
the divine nature must not on any account
be adduced to explain this, but must be kept
free from the task and in perfect bliss.
Unless this be done, the whole study of celestial
phenomena will be in vain, as indeed it has
proved to be with some who did not lay hold
of a possible method, but fell into the folly
of supposing that these events happen in
one single way only and of rejecting all
the others which are possible, suffering
themselves to be carried into the realm of
the unintelligible,. and being unable to
take a comprehensive view of the facts which
must be taken as clues to the rest.
The variations in the length of nights and
days may be due to the swiftness and again
to the slowness of the sun's motion in the
sky, owing to the variations in the length
of spaces traversed and to his accomplishing
some distances more swiftly or more slowly,
as happens sometimes within our own experience;
and with these facts our explanation of celestial
phenomena must agree; whereas those who adopt
only one explanation are in conflict with
the facts and are utterly mistaken as to
the way in which man can attain knowledge.
The signs in the sky which betoken the weather
may be due to mere coincidence of the seasons,
as is the case with signs from animals seen
on earth, or they may be caused by changes
and alterations in the air. For neither the
one explanation nor the other is in conflict
with facts, and it is not easy to see in
which cases the effect is due to one cause
or to the other.
Clouds may form and gather either because
the air is condensed under the pressure of
winds, or because atoms which hold together
and are suitable to produce this result become
mutually entangled, or because currents collect
from tile earth and the waters ; and there
are several other ways in which it is not
impossible for the aggregations of such bodies
into clouds to be brought about. And that
being so, rain may be produced from them
sometimes by their compression, sometimes
by their transformation; or again may be
caused by exhalations of moisture rising
from suitable places through the air, while
a more violent inundation is due to certain
accumulations suitable for such discharge.
Thunder may be due to the rolling of wind
in the hollow parts of the clouds, as it
is sometimes imprisoned in vessels which
we use; or to the roaring of fire in them
when blown by a wind, or to the rending and
disruption of clouds, or to the friction
and splitting up of clouds when they have
become as firm as ice.
As in the whole survey, so in this particular
point, the facts invite us to give a plurality
of explanations. Lightning too happens in
a variety of ways. For when the clouds rub
against each other and collide, that collocation
of atoms which is the cause of fire generates
lightning; or it may be due to the flashing
forth from the clouds, by reason of winds,
of particles capable of producing this brightness;
or else it is squeezed out of the clouds
when they have been condensed either by their
own action or by that of the winds; or again,
the light diffused from the stars may be
enclosed in the clouds, then driven about
by their motion and by that of the winds,
and finally make its escape from the clouds;
or light of the finest texture may be filtered
through the clouds (whereby the clouds may
be set on fire and thunder produced), and
the motion of this light may make lightning;
or it may arise from the combustion of wind
brought about by the violence of its motion
and the intensity of its compression; or,
when the clouds are rent asunder by winds,
and the atoms which generate fire are expelled,
these likewise cause lightning to appear.
And it may easily be seen that its occurrence
is possible in many other ways, so long as
we hold fast to facts and take a general
view of what is analogous to them. Lightning
precedes thunder, when the clouds are constituted
as mentioned above and the configuration
which produces lightning is expelled at the
moment when the wind falls upon the cloud,
and the wind being rolled up afterwards produces
the roar of thunder; or, if both are simultaneous,
the lightning moves with a greater velocity
towards its and the thunder lags behind,
exactly as when persons who are striking
blows are observed from a distance. A thunderbolt
is caused when winds are repeatedly collected,
imprisoned, and violently ignited; or when
a part is torn asunder and is more violently
expelled downwards, the rending being due
to the fact that the compression of the clouds
has made the neighboring parts more dense;
or again it may be due like thunder merely
to the expulsion of the imprisoned fire,
when this has accumulated and been more violently
inflated with wind and has torn the cloud,
being unable to withdraw to the adjacent
parts because it is continually more and
more closely compressed [generally by some
high mountain where thunderbolts mostly fall].
And there are several other ways in which
thunderbolts may possibly be produced. Exclusion
of myth is the sole condition necessary;
and it will be excluded, if one properly
attends to the facts and hence draws inferences
to interpret what is obscure.
Fiery whirlwinds are due to the descent of
a cloud forced downwards like a pillar by
the wind in full force and carried by a gale
round and round, while at the same time the
outside wind gives the cloud a lateral thrust;
or it may be due to a change of the wind
which veers to all points of the compass
as a current of air from above helps to force
it to move; or it may be that a strong eddy
of winds has been started and is unable to
burst through laterally because the air around
is closely condensed. And when they descend
upon land, they cause what are called tornadoes,
in accordance with the various ways in which
they are produced through the force of the
wind; and when let down upon the sea, they
cause waterspouts.
Earthquakes may be due to the imprisonment
of wind underground, and to its being interspersed
with small masses of earth and then set in
continuous motion, thus causing the earth
to tremble. And the earth either takes in
this wind from without or from the falling
in of foundations, when undermined, into
subterranean caverns, thus raising a wind
in the imprisoned air. Or they may be due
to the propagation of movement arising from
the fall of many foundations and to its being
again checked when it encounters the more
solid resistance of earth. And there are
many other causes to which these oscillations
of the earth may be due.
Winds arise from time to time when foreign
matter continually and gradually finds its
way into the air; also through the gathering
of great store of water. The rest of the
winds arise when a few of them fall into
the many hollows and they are thus divided
and multiplied.
Hail is caused by the firmer congelation
and complete transformation, and subsequent
distribution into drops, of certain particles
resembling wind : also by the slighter congelation
of certain particles of moisture and the
vicinity of certain particles of wind which
at one and the same time forces them together
and makes them burst, so that they become
frozen in parts and in the whole mass. The
round shape of hailstones is not impossibly
due to the extremities on all sides being
melted and to the fact that, as explained,
particles either of moisture or of wind surround
them evenly on all sides and in every quarter,
when they freeze.
Snow may be formed when a fine rain issues
from the clouds because the pores are symmetrical
and because of the continuous and violent
pressure of the winds upon clouds which are
suitable; and then this rain has been frozen
on its way because of some violent change
to coldness in the regions below the clouds.
Or again, by congelation in clouds which
have uniform density a fall of snow might
occur through the clouds which contain moisture
being densely packed in close proximity to
each other; and these clouds produce a sort
of compression and cause hail, and this happens
mostly in spring. And when frozen clouds
rub against each other., this accumulation
of snow might be thrown off. And there are
other ways in which snow might be formed.
Dew is formed when such particles as are
capable of producing this sort of moisture
meet each other from the air: again by their
rising from moist and damp places, the sort
of place where dew is chiefly formed, and
their subsequent coalescence, so as to create
moisture and fall downwards, just as in several
cases something similar is observed to take
place under our eyes. And the formation of
hoar-frost is not different from that of
dew, certain particles of such a nature becoming
in some such way congealed owing to a certain
condition of cold air.
Ice is formed by the expulsion from the water
of the circular, and the compression of the
scalene and acute-angled atoms contained
in it; further by the accretion of such atoms
from without, which being driven together
cause the water to solidify after the expulsion
of a certain number of round atoms.
The rainbow arises when the sun shines upon
humid air; or again by a certain peculiar
blending of light with air, which will cause
either all the distinctive qualities of these
colors or else some of them belonging to
a single kind, and from the reflection of
this light the air all around will be colored
as we see it to be, as the sun shines upon
its parts. The circular shape which it assumes
is due to the fact that the distance of every
point is perceived by our sight to be equal;
or it may be because, the atoms in the air
or in the clouds and deriving from the sun
having been thus united, the aggregate of
them presents a sort of roundness.
A halo round the moon arises because the
air on all sides extends to the moon; or
because it equably raises upwards the currents
from the moon so high as to impress a circle
upon the cloudy mass and not to separate
it altogether; or because it raises the air
which immediately surrounds the moon symmetrically
from all sides up to a circumference round
her and there forms a thick ring. And this
happens at certain parts either because a
current has forced its wry in from without
or because the heat has gained possession
of certain passages in order to effect this.
Comets arise either because fire is nourished
in certain places at certain intervals in
the heavens, if circumstances are favorable;
or because at times the heaven has a particular
motion above us so that such stars appear;
or because the stars themselves are set in
motion under certain conditions and come
to our neighborhood and show themselves.
And their disappearance is due to the causes
which are the opposite of these. Certain
stars may revolve without setting not only
for the reason alleged by some, because this
is the part of the world round which, itself
unmoved, the rest revolves, but it may also
be because a circular eddy of air surrounds
this part, which prevents them from traveling
out of sight like other stars or because
there is a dearth of necessary fuel farther
on, while there is abundance in that part
where they are seen to be. Moreover there
are several other ways in which this might
be brought about, as may be seen by anyone
capable of reasoning in accordance with the
facts.
The wanderings of certain stars, if such
wandering is their actual motion, and the
regular movement of certain other stars,
may be accounted for by saying that they
originally moved in a circle and were constrained,
some of them to be whirled round with the
same uniform rotation and others with a whirling
motion which varied; but it may also be that
according to the diversity of the regions
traversed in some places there are uniform
tracts of air, forcing them forward in one
direction and burning uniformly, in others
these tracts present such irregularities
4s cause the motions observed. To assign
a single cause for these effects when the
facts suggest several causes is madness and
a strange inconsistency; yet it is done by
adherents of rash astronomy, who assign meaningless
causes for the stars whenever they persist
in saddling the divinity with burdensome
tasks. That certain stars are seen to be
left behind by others may be because they
travel more slowly, though they go the same
round as the others; or it may be that they
are drawn back by the same whirling motion
and move in the opposite direction; or again
it may be that some travel over a larger
and others over a smaller space in making
the same revolution. But to lay down as assured
a single explanation of these phenomena is
worthy of those who seek to dazzle the multitude
with marvels.
Falling stars, as they are called, may in
some cases be due to the mutual friction
of the stars themselves, in other cases to
the expulsion of certain parts when that
mixture of fire and air takes place which
was mentioned when we were discussing lightning;
or it may be due to the meeting of atoms
capable of generating fire, which accord
so well as to produce this result, and their
subsequent motion wherever the impulse which
brought them together at first leads them;
or it may be that wind collects in certain
dense mist-like masses and, since it is imprisoned,
ignites and then bursts forth upon whatever
is round about it, and is carried to that
place to which its motion impels it. And
there are other ways in which this can be
brought about without recourse to myths.
The fact that the weather is sometimes foretold
from the behavior of certain animals is a
mere coincidence in time. For the animals
offer no necessary reason why a storm should
be produced and no divine being sits observing
when these animals go out and afterwards
fulfilling the signs which they have given.
For such folly as this would not possess
the most ordinary being if ever so little
enlightened, much less one who enjoys perfect
felicity.
All this, Pythocles, you should keep in mind;
for then you will escape a long way from
myth, and you will be able to view in their
connection the instances which are similar
to these. But above all give yourself up
to the study of first principles and of infinity
and of kindred subjects, and further of the
standards and of the feelings and of the
end for which we choose between them. For
to study these subjects together will easily
enable you to understand the causes of the
particular phenomena. And those who have
not fully accepted this, in proportion as
they have not done so, will be ill acquainted
with these very subjects, nor have they secured
the end for which they ought to be studied.
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Evans Experientialism 
