A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun’s very center.

It is here that is to be found the source of the energy that the Sun constantly pours out into space as light and heat. This energy is liberated at the center of the Sun as billions upon billions of nuclei of hydrogen atoms collide with each other and fuse together to form nuclei of helium, and in doing so, release some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun requires that some 600 million tons of hydrogen be converted into helium in the Sun every second. This the Sun has been doing for several thousands of millions of years. The nuclear energy is released at the Sun’s center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun to be reemitted at slightly longer wavelengths. This radiation, in its turn is absorbed and reemitted. As the energy filters through the layers of the solar interior, it passes through the X-ray part of the spectrum eventually becoming light. At this stage, it has reached what we call the solar surface, and can escape into space without being absorbed further by solar atoms. A very small fraction of the Sun’s light and heat is emitted in such directions that after passing unhindered through interplanetary space, it hits the Earth.

能量的来源

概说生命的物理和化学特性必须始于太阳--确切地说，是太阳的核心，而非地球。 能量来自太阳的核心。

在这里，太阳不停地以光和热的形式向空间倾泻出能量。 数十亿计的 氢原子核在太阳的核心碰撞并且聚变生成氦。 在此过程中一部分原本储存于原子核中的能量被释放出来。 太阳所产生的光和热需要每秒将六亿吨氢转化为氦。 这样的转化在太阳中已经持续几十亿年了。核能在太阳的核心被释放为高能的伽马射线。这是一种电磁射线， 就象光波和无线电波一样，只是波长要短得多。这种伽玛射线被太阳内的??。 这新的射线再次被吸收，而后释放。 在能量由太阳内部一层层渗透出来的过程中，它经过了光谱中 X 射线部分，最后变成了光。在此阶段，能量到达我们所称的太阳表层，并且离散到空间而不再被太阳原子所吸收。只有很小一部分 太阳的光和热由此方向释放出来，并且未被阻挡，穿越星空，来到地球。

Vision

Human vision like that of other pr mates has evolved in an arboreal environment. In the dense complex world of a tropical forest, it is more important to see well than to develop an acute sense of smell.

In the course of evolution members of the primate line have acquired large eyes while the snout has shrunk to give the eye an unimpeded view. Of mammals only humans and some primates enjoy color vision. The red flag is black to the bull. Horses live in a monochrome world Light visible to human eyes however occupies only a very narrow band in the whole electromagnetic spectrum. Ultraviolet rays are invisible to humans though ants and honeybees are sensitive to them. Humans have no direct perception of infrared rays unlike the rattlesnake which has receptors tuned into wavelengths longer than 0.7 micron. The world would look eerily different if human eyes were sensitive to infrared radiation. Then instead of the darkness of night, we would be able to move easily in a strange shadowless world where objects glowed with varying degrees of intensity.

But human eyes excel in other ways. They are in fact remarkably discerning in color gradation. The color sensitivity of normal human vision is rarely surpassed even by sophisticated technical devices.

视觉

人类的视觉，和其它灵长目动物的一样，是在丛林环境中进化出来的。在稠密、复杂 的热带丛林里，好的视觉比灵敏的嗅觉更加重要。

在进化过程中，灵长目动物的眼睛变大，同时鼻子变小以使视野不受阻碍。在哺乳类动物中，只有人和一些灵长目动物能够分辨颜色。红旗在公牛看来是黑色的，马则生活在一个单色的世界里。 然而，人眼可见的光在整个光谱中只占一个非常狭窄的频段。人是看不到紫外线的，尽管蚂蚁和蜜蜂可以感觉到。与 响尾蛇不同，人也不能直接感受到红外线。响尾蛇的感觉器可以感受波长超过 0.7 微米的光线。如果人能感受到红外线的话，这世界看上去将十分不同，而且恐怖。 到那时，将与夜的黑暗相反，我们能轻易地在一个奇异的没有阴影的世界里走动。 任何物体都强弱不等 地闪着光。

然而，人眼在其它方面有优越之处。事实上，人眼对颜色梯度具有非凡的分辨 能力。普通人类的视觉感受色彩的灵敏程度，甚至连精密的技术装备都很难超越。