Section XVII

The effects of blackness.

Blackness is but a partial darkness; and therefore it derives¹ some of its powers from being mixed and surrounded with colored bodies. In its own nature, it cannot be considered as a color. Black bodies, reflecting none, or but a few rays, with regard to sight, are but as so many vacant spaces, dispersed² among the objects we view. When the eye lights on one of these vacuities, after having been kept in some degree of tension by the play of the adjacent colors upon it, it suddenly falls into a relaxation³; out of which it as suddenly recovers by a convulsive spring. To illustrate⁴ this: let us consider that when we intend to sit on a chair, and find it much lower than was expected, the shock is very violent; much more violent than could be thought from so slight a fall as the difference between one chair and another can possibly make. If, after descending⁵ a flight of stairs, we attempt inadvertently to take another step in the manner of the former ones, the shock is extremely rude and disagreeable: and by no art can we cause such a shock by the same means when we expect and prepare for it. When I say that this is owing to having the change made contrary to expectation; I do not mean solely⁶, when the mind expects. I mean likewise, that when any organ of sense is for some time affected⁷ in some one manner, if it be suddenly affected otherwise, there ensues a convulsive motion; such a convulsion as is caused when anything happens against the expectance of the mind. And though it may appear strange that such a change as produces a relaxation should immediately produce a sudden convulsion; it is yet most certainly so, and so in all the senses. Every one knows that sleep is a relaxation; and that silence, where nothing keeps the organs of hearing in action, is in general fittest to bring on this relaxation; yet when a sort of murmuring sounds dispose a man to sleep, let these sounds cease suddenly, and the person immediately awakes; that is, the parts are braced⁸ up suddenly, and he awakes. This I have often experienced myself, and I have heard the same from observing persons. In like manner, if a person in broad daylight were falling asleep, to introduce a sudden darkness would prevent his sleep for that time, though silence and darkness in themselves, and not suddenly introduced, are very favorable to it. This I knew only by conjecture⁹ on the analogy of the senses when I first digested these observations; but I have since experienced it. And I have often experienced, and so have a thousand others, that on the first inclining towards sleep, we have been suddenly awakened¹⁰ with a most violent start; and that this start was generally preceded by a sort of dream of our falling down a precipice¹¹: whence does this strange motion arise, but from the too sudden relaxation of the body, which by some mechanism¹² in nature restores itself by as quick and vigorous an exertion¹⁴ of the contracting power of the muscles? The dream itself is caused by this relaxation; and it is of too uniform a nature to be attributed to any other cause. The parts relax too suddenly, which is in the nature of falling; and this accident of the body induces this image in the mind. When we are in a confirmed state of health and vigor¹³, as all changes are then less sudden, and less on the extreme, we can seldom complain of this disagreeable sensation.

1 derives   

v.得到( derive的第三人称单数 )；（从…中）得到获得；源于；（从…中）提取

参考例句：

• English derives in the main from the common Germanic stock. 英语主要源于日耳曼语系。 来自《简明英汉词典》
• He derives his income from freelance work. 他以自由职业获取收入。 来自《简明英汉词典》

2 dispersed   

adj. 被驱散的, 被分散的, 散布的

参考例句：

• The clouds dispersed themselves. 云散了。
• After school the children dispersed to their homes. 放学后，孩子们四散回家了。

3 relaxation   

n.松弛，放松；休息；消遣；娱乐

参考例句：

• The minister has consistently opposed any relaxation in the law.部长一向反对法律上的任何放宽。
• She listens to classical music for relaxation.她听古典音乐放松。

4 illustrate   

v.举例说明，阐明；图解，加插图

参考例句：

• The company's bank statements illustrate its success.这家公司的银行报表说明了它的成功。
• This diagram will illustrate what I mean.这个图表可说明我的意思。

5 descending   

n. 下行 adj. 下降的

参考例句：

• The results are expressed in descending numerical order . 结果按数字降序列出。
• The climbers stopped to orient themselves before descending the mountain. 登山者先停下来确定所在的位置，然后再下山。

6 solely   

adv.仅仅，唯一地

参考例句：

• Success should not be measured solely by educational achievement.成功与否不应只用学业成绩来衡量。
• The town depends almost solely on the tourist trade.这座城市几乎完全靠旅游业维持。

7 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。

8 braced   

adj.拉牢的v.支住( brace的过去式和过去分词 )；撑牢；使自己站稳；振作起来

参考例句：

• They braced up the old house with balks of timber. 他们用梁木加固旧房子。 来自《简明英汉词典》
• The house has a wooden frame which is braced with brick. 这幢房子是木结构的砖瓦房。 来自《简明英汉词典》

9 conjecture   

n./v.推测，猜测

参考例句：

• She felt it no use to conjecture his motives.她觉得猜想他的动机是没有用的。
• This conjecture is not supported by any real evidence.这种推测未被任何确切的证据所证实。

10 awakened   

v.（使）醒( awaken的过去式和过去分词 )；（使）觉醒；弄醒；（使）意识到

参考例句：

• She awakened to the sound of birds singing. 她醒来听到鸟的叫声。
• The public has been awakened to the full horror of the situation. 公众完全意识到了这一状况的可怕程度。 来自《简明英汉词典》

11 precipice   

n.悬崖，危急的处境

参考例句：

• The hut hung half over the edge of the precipice.那间小屋有一半悬在峭壁边上。
• A slight carelessness on this precipice could cost a man his life.在这悬崖上稍一疏忽就会使人丧生。

12 mechanism   

n.机械装置；机构，结构

参考例句：

• The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
• The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。

13 vigor   

n.活力，精力，元气

参考例句：

• The choir sang the words out with great vigor.合唱团以极大的热情唱出了歌词。
• She didn't want to be reminded of her beauty or her former vigor.现在，她不愿人们提起她昔日的美丽和以前的精力充沛。

14 exertion   

n.尽力，努力

参考例句：

• We were sweating profusely from the exertion of moving the furniture.我们搬动家具大费气力，累得大汗淋漓。
• She was hot and breathless from the exertion of cycling uphill.由于用力骑车爬坡，她浑身发热。