'Conservation' (the conservation law) means this ... that there is a number, which you can calculate, at one moment-and as nature undergoes its multitude of changes, this number doesn't change. That is, if you calculate again, this quantity, it'll be the same as it was before. An example is the conservation of energy: there's a quantity that you can calculate according to a certain rule, and it comes out the same answer after, no matter what happens, happens.

The basis of action on love, the brotherhood of all men, the value of the individual... the humility of the spirit.

There is no harm in doubt and skepticism, for it is through these that new discoveries are made.

That is the logical tight-rope on which we have to walk if we wish to interpret nature.

From a long view of the history of mankind, seen from, say, ten thousand years from now, there can be little doubt that the most significant event of the 19th century will be judged as Maxwell's discovery of the laws of electrodynamics. The American Civil War will pale into provincial insignificance in comparison with this important scientific event of the same decade.

I don't feel frightened by not knowing things.

The first principle is that you must not fool yourself and you are the easiest person to fool.