Scientific achievements seem evanescent, because the very progress of science causes their supersedure; yet some of them are of so fundamental a nature that they are immortal in a deeper way.

The whole past and the whole world are alive in my heart, and I shall do my part to communicate their presence to my readers.

Some forty years of experience in my field as a scholar and as a teacher have given me great confidence mixed with greater humility.

The historical order is very interesting, but accidental and capricious; if we would to understand the growth of knowledge, we cannot be satisfied with accidents, we must explain how knowledge was gradually built up.

On the basis of my historical experience, I fully believe that mathematics of the 25th century will be as different from that of today as the latter is from that of the 16th century.

Wisdom is not mathematical, nor astronomical, nor zoological; when it talks too much of any one thing it ceases to be itself. There are wise physicists, but wisdom is not physical; there are wise physicians, but wisdom is not medical.

If we are generous enough, we can stretch our souls everywhere and everywhen else. If we succeed in doing so, we shall discover that our present embraces the past and the future and that the whole world is our province.

I am obliged to deal with hundreds of men and to make them live without killing the reader.

The whole iconography of ancient science is simply the fruit of wishful thinking.

A deed happens in a definite place at a definite time, but if it be sufficiently great and pregnant, its virtue radiates everywhere in time and space.