A teacher affects eternity; he can never tell where his influence stops.

His brothers were the type; he was the variation.

We shall some day catch an abstract truth by the tail, and then we shall have our religion and our immortality.

[P]olitical and social and scientific values ... should be correlated in some relation of movement that could be expressed in mathematics, nor did one care in the least that all the world said it could not be done, or that one knew not enough mathematics even to figure a formula beyond the schoolboy s=(1/2)gt2. If Kepler and Newton could take liberties with the sun and moon, an obscure person ... could take liberties with Congress, and venture to multiply its attraction into the square of its time. He had only to find a value, even infinitesimal, for its attraction.

One friend in a lifetime is much; two are many; three are hardly possible.

Accident counts for as much in companionship as in marriage.

Of all studies, the one he would rather have avoided was that of his own mind. He knew no tragedy so heartrending as introspection.