ed man had learned to use the skins of animals to cover them.
Then about 10 years ago, under this standard, man emerged from his caves to construct other kinds of shelter.
Only five years ago man learned to write and use a cart with wheels.
Christianity began less than two years ago.
没人能够断言我们能走多远，能走多快。但如果你愿意，将5万年的人类历史浓缩为短短的半个世纪。
在这个时间跨度下，我们对于开始的40年知之甚少，除了在最后阶段我们学会了用兽皮遮体。
接下来，在此标准之下，10年前，人类走出洞穴，开始建造新的家园。
五年前人类才学会了写字和使用有轮子的车辆。
基督教产生于不到两年前。
The printing press came this year, and then less than two months ago, during this whole 50-year span of human history, the steam engine provided a new source of power.
Newton explored the meaning of gravity.
Last month electric lights and telephones and automobiles and airplanes became available.
Only last week did we develop penicillin and television and nuclear power, and now if America\''s new spacecraft succeeds in reaching Venus, we will literally reached the stars before midnight tonight.
印刷出版今年才出现。在人类历史的50年间，在不到两个月前，蒸汽机为我们提供了新的动力。
牛顿发现了引力的意义。
上个月，电灯，电话，汽车和飞机成为了现实。
仅仅上周我们才发明了盘尼西林（即青霉素，译者注），电视与核能。如果现在美国最新的飞船能够成功抵达金星，那么我们才真正算得上在今天午夜抵达其他星球了。
This is a breathtaking pace, and such a pace cannot help but create new ills as it dispels old, new ignorance, new problems, new dangers.
Surely the opening vistas of space promise high costs and hardships, as well as high reward.
So it is not surprising that some would have us stay where we are a little longer to rest, to wait.
这是激动人心的一步，但迈出的这一步在驱散旧邪恶的同时，也会派生出新邪恶，新无知、新问题和新危险。
太空所展现的远景固然会得到巨大的回报，但同时也会伴随着巨大的困难与高昂的代价。
所以并不意外，有时我们会在裹足不前，焦急等待。
But this city of Houston, this state of Texas, this country of the United States was not built by those who waited and rested and wished to look behind them.
This country was conquered by those who moved forward--and so will space.
William Bradford, speaking in