Book II Chapter 7

The object of sight is the visible, and what is visible is (a) colour and (b) a certain kind of object which can be described in words but which has no single name; what we mean by (b) will be abundantly clear as we proceed. Whatever is visible is colour and colour is what lies upon what is in its own nature visible; ‘in its own nature’ here means not that visibility is involved in the definition of what thus underlies¹ colour, but that that substratum contains in itself the cause of visibility. Every colour has in it the power to set in movement what is actually transparent²; that power constitutes its very nature. That is why it is not visible except with the help of light; it is only in light that the colour of a thing is seen. Hence our first task is to explain what light is.

Now there clearly is something which is transparent, and by ‘transparent’ I mean what is visible, and yet not visible in itself, but rather owing its visibility to the colour of something else; of this character are air, water, and many solid bodies. Neither air nor water is transparent because it is air or water; they are transparent because each of them has contained in it a certain substance which is the same in both and is also found in the eternal body which constitutes the uppermost shell of the physical Cosmos³. Of this substance light is the activity-the activity of what is transparent so far forth⁴ as it has in it the determinate power of becoming transparent; where this power is present, there is also the potentiality of the contrary, viz. darkness. Light is as it were the proper colour of what is transparent, and exists whenever the potentially transparent is excited to actuality by the influence of fire or something resembling ‘the uppermost body’; for fire too contains something which is one and the same with the substance in question.

We have now explained what the transparent is and what light is; light is neither fire nor any kind whatsoever⁵ of body nor an efflux from any kind of body (if it were, it would again itself be a kind of body)-it is the presence of fire or something resembling fire in what is transparent. It is certainly not a body, for two bodies cannot be present in the same place. The opposite of light is darkness; darkness is the absence from what is transparent of the corresponding positive state above characterized; clearly therefore, light is just the presence of that.

Empedocles (and with him all others who used the same forms of expression) was wrong in speaking of light as ‘travelling’ or being at a given moment between the earth and its envelope, its movement being unobservable by us; that view is contrary both to the clear evidence of argument and to the observed facts; if the distance traversed were short, the movement might have been unobservable, but where the distance is from extreme East to extreme West, the draught⁶ upon our powers of belief is too great.

What is capable of taking on colour is what in itself is colourless, as what can take on sound is what is soundless; what is colourless includes (a) what is transparent and (b) what is invisible or scarcely visible, i.e. what is ‘dark’. The latter (b) is the same as what is transparent, when it is potentially, not of course when it is actually transparent; it is the same substance which is now darkness, now light.

Not everything that is visible depends upon light for its visibility. This is only true of the ‘proper’ colour of things. Some objects of sight which in light are invisible, in darkness stimulate⁷ the sense; that is, things that appear fiery⁸ or shining. This class of objects has no simple common name, but instances of it are fungi⁹, flesh, heads, scales, and eyes of fish. In none of these is what is seen their own proper’ colour. Why we see these at all is another question. At present what is obvious is that what is seen in light is always colour. That is why without the help of light colour remains¹⁰ invisible. Its being colour at all means precisely¹¹ its having in it the power to set in movement what is already actually transparent, and, as we have seen, the actuality of what is transparent is just light.

The following experiment makes the necessity of a medium clear. If what has colour is placed in immediate¹² contact with the eye, it cannot be seen. Colour sets in movement not the sense organ but what is transparent, e.g. the air, and that, extending continuously from the object to the organ, sets the latter in movement. Democritus misrepresents the facts when he expresses the opinion that if the interspace were empty one could distinctly see an ant on the vault¹³ of the sky; that is an impossibility. Seeing is due to an affection or change of what has the perceptive¹⁴ faculty¹⁵, and it cannot be affected¹⁶ by the seen colour itself; it remains that it must be affected by what comes between. Hence it is indispensable that there be something in between-if there were nothing, so far from seeing with greater distinctness, we should see nothing at all.

We have now explained the cause why colour cannot be seen otherwise than in light. Fire on the other hand is seen both in darkness and in light; this double possibility follows necessarily from our theory, for it is just fire that makes what is potentially transparent actually transparent.

The same account holds also of sound and smell; if the object of either of these senses is in immediate contact with the organ no sensation is produced. In both cases the object sets in movement only what lies between, and this in turn sets the organ in movement: if what sounds or smells is brought into immediate contact with the organ, no sensation will be produced. The same, in spite of all appearances, applies also to touch and taste; why there is this apparent difference will be clear later. What comes between in the case of sounds is air; the corresponding medium in the case of smell has no name. But, corresponding to what is transparent in the case of colour, there is a quality found both in air and water, which serves as a medium for what has smell-I say ‘in water’ because animals that live in water as well as those that live on land seem to possess the sense of smell, and ‘in air’ because man and all other land animals that breathe, perceive smells only when they breathe air in. The explanation of this too will be given later.

1 underlies   

v.位于或存在于（某物）之下( underlie的第三人称单数 )；构成…的基础（或起因），引起

参考例句：

• I think a lack of confidence underlies his manner. 我认为他表现出的态度是因为他缺乏信心。 来自《简明英汉词典》
• Try to figure out what feeling underlies your anger. 努力找出你的愤怒之下潜藏的情感。 来自辞典例句

2 transparent   

adj.明显的，无疑的；透明的

参考例句：

• The water is so transparent that we can see the fishes swimming.水清澈透明，可以看到鱼儿游来游去。
• The window glass is transparent.窗玻璃是透明的。

3 cosmos   

n.宇宙；秩序，和谐

参考例句：

• Our world is but a small part of the cosmos.我们的世界仅仅是宇宙的一小部分而已。
• Is there any other intelligent life elsewhere in the cosmos?在宇宙的其他星球上还存在别的有智慧的生物吗？

4 forth   

adv.向前；向外，往外

参考例句：

• The wind moved the trees gently back and forth.风吹得树轻轻地来回摇晃。
• He gave forth a series of works in rapid succession.他很快连续发表了一系列的作品。

5 whatsoever   

adv.（用于否定句中以加强语气）任何；pron.无论什么

参考例句：

• There's no reason whatsoever to turn down this suggestion.没有任何理由拒绝这个建议。
• All things whatsoever ye would that men should do to you,do ye even so to them.你想别人对你怎样，你就怎样对人。

6 draught   

n.拉，牵引，拖；一网（饮，吸，阵)；顿服药量，通风；v.起草，设计

参考例句：

• He emptied his glass at one draught.他将杯中物一饮而尽。
• It's a pity the room has no north window and you don't get a draught.可惜这房间没北窗，没有过堂风。

7 stimulate   

vt.刺激，使兴奋；激励，使…振奋

参考例句：

• Your encouragement will stimulate me to further efforts.你的鼓励会激发我进一步努力。
• Success will stimulate the people for fresh efforts.成功能鼓舞人们去作新的努力。

8 fiery   

adj.燃烧着的，火红的；暴躁的；激烈的

参考例句：

• She has fiery red hair.她有一头火红的头发。
• His fiery speech agitated the crowd.他热情洋溢的讲话激动了群众。

9 fungi   

n.真菌，霉菌

参考例句：

• Students practice to apply the study of genetics to multicellular plants and fungi.学生们练习把基因学应用到多细胞植物和真菌中。
• The lawn was covered with fungi.草地上到处都是蘑菇。

10 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

11 precisely   

adv.恰好，正好，精确地，细致地

参考例句：

• It's precisely that sort of slick sales-talk that I mistrust.我不相信的正是那种油腔滑调的推销宣传。
• The man adjusted very precisely.那个人调得很准。

12 immediate   

adj.立即的；直接的，最接近的；紧靠的

参考例句：

• His immediate neighbours felt it their duty to call.他的近邻认为他们有责任去拜访。
• We declared ourselves for the immediate convocation of the meeting.我们主张立即召开这个会议。

13 vault   

n.拱形圆顶，地窖，地下室

参考例句：

• The vault of this cathedral is very high.这座天主教堂的拱顶非常高。
• The old patrician was buried in the family vault.这位老贵族埋在家族的墓地里。

14 perceptive   

adj.知觉的，有洞察力的，感知的

参考例句：

• This is a very perceptive assessment of the situation.这是一个对该情况的极富洞察力的评价。
• He is very perceptive and nothing can be hidden from him.他耳聪目明，什么事都很难瞒住他。

15 faculty   

n.才能；学院，系；(学院或系的)全体教学人员

参考例句：

• He has a great faculty for learning foreign languages.他有学习外语的天赋。
• He has the faculty of saying the right thing at the right time.他有在恰当的时候说恰当的话的才智。

16 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。