It is hard for us to realize nowadays how difficult it was for the pioneers.

我们今天很难想像昔日的登山先驱们是多么艰苦。

local epidemics of this disease could be created.

就可以使这种疾病在一个地区蔓延起来。

First the electroencephalograph (which is simply a device for recording the electrical activity of the brain by attaching electrodes to the scalp) shows that while there is a change in the pattern of activity during sleep,

第一点，脑电图记录仪（不过是一种把电极接到头皮上记录脑电活动的仪器）显示，人在睡眠时大脑活动的方式有变化，

It is almost always due to some very special circumstances that traces of land animals survive,

几乎总是由于某些特殊的条件，陆地动物的遗体才被存下来，

Today, although the old Galileo lives on in many popular writings,

今天，虽然已故的伽利略继续活在许多通俗读物中，

wind, earth movements or tremors, and the gravitational pull of the moon and the sun.

风、地球的运动或震颤和月亮、太阳的引力。