The floating vapour is just as true an illustration of the law of gravity as the falling avalanche.

The spirit of man can endure only so much and when it is broken only a miracle can mend it.

The fuel in the earth will be exhausted in a thousand or more years, and its mineral wealth, but man will find substitutes for these in the winds, the waves, the sun's heat, and so forth.

[Theodore Roosevelt] was a naturalist on the broadest grounds, uniting much technical knowledge with knowledge of the daily lives and habits of all forms of wild life. He probably knew tenfold more natural history than all the presidents who had preceded him, and, I think one is safe in saying, more human history also.

Joy in the universe, and keen curiosity about it all - that has been my religion.

Almost all of the governments have agreed that they will not acquire nuclear weapons and that they will allow the International Atomic Energy Agency to monitor their commercial and research nuclear power operations to ensure that nuclear materials - highly enriched uranium and plutonium - are not diverted to use in weapons.

There is an international treaty framework for this. It's the Nuclear Non-Proliferation Treaty (NPT). Most countries in the world are members of the treaty.