The more experiences and experiments accumulate in the exploration of nature, the more precarious the theories become. But it is not always good to discard them immediately on this account. For every hypothesis which once was sound was useful for thinking of previous phenomena in the proper interrelations and for keeping them in context. We ought to set down contradictory experiences separately, until enough have accumulated to make building a new structure worthwhile.

A vacuum of ideas affects people differently than a vacuum of air, otherwise readers of books would be constantly collapsing.

It often takes more courage to change one's opinion than to stick to it.

One's first step in wisdom is to question everything - and one's last is to come to terms with everything.

Delicacy in woman is strength.

I have never yet met anyone who did not think it was an agreeable sensation to cut tinfoil with scissors.

Just as the performance of the vilest and most wicked deeds requires spirit and talent, so even the greatest demand a certain insensitivity which under other circumstances we would call stupidity.