"Frege, Gottlob (1848 - 1925)
A scientist can hardly meet with anything more undesirable than to have the foundations give way just as the work is finished. I was put in this position by a letter from Mr. Bertrand Russell when the work was nearly through the press.
In Scientific American, May 1984, p 77."

"Frederick the Great (1712-1786)
To your care and recommendation am I indebted for having replaced a half-blind mathematician with a mathematician with both eyes, which will especially please the anatomical members of my Academy.
[To D'Alembert about Lagrange. Euler had vacated the post.]
In D. M. Burton, Elementary Number Theory, Boston: Allyn and Bacon, Inc., 1976."

"Eves, Howard W.
One is hard pressed to think of universal customs that man has successfully established on earth. There is one, however, of which he can boast the universal adoption of the Hindu-Arabic numerals to record numbers. In this we perhaps have man's unique worldwide victory of an idea.
Mathematical Circles Squared, Boston: Prindle, Weber and Schmidt, 1972."

"Euler, Leonhard (1707-1783)
[upon losing the use of his right eye]
Now I will have less distraction.
In H. Eves In Mathematical Circles, Boston: Prindle, Weber and Schmidt, 1969."

"Einstein, Albert (1879-1955)
The human mind has first to construct forms, independently, before we can find them in things."

"Einstein, Albert (1879-1955)
Since the mathematicians have invaded the theory of relativity, I do not understand it myself anymore.
In A. Sommerfelt 'To Albert Einstein's Seventieth Birthday' in Paul A. Schilpp (ed.) Albert Einstein, Philosopher-Scientist, Evanston, 1949."

"Einstein, Albert (1879-1955)
Gott wuerfelt nicht."

"Einstein, Albert (1879-1955)
[During a lecture:]This has been done elegantly by Minkowski; but chalk is cheaper than grey matter, and we will do it as it comes.
[Attributed by Polya.]
J.E. Littlewood, A Mathematician's Miscellany, Methuen and Co. Ltd., 1953."

"Eddington, Sir Arthur (1882-1944)
I believe there are 15,747,724,136,275,002,577,605,653,961,181,555,468,044,717,914,527,116,709,366,231,425,076,185,631,031,296 protons in the universe and the same number of electrons.
The Philosophy of Physical Science. Cambridge, 1939."

"Eddington, Sir Arthur (1882-1944)
Proof is the idol before whom the pure mathematician tortures himself.
In N. Rose Mathematical Maxims and Minims, Raleigh NC: Rome Press Inc., 1988."

Descartes Rene, (1596-1650)

"I thought the following four [rules] would be enough, provided that I made a firm and constant resolution not to fail even once in the observance of them. The first was never to accept anything as true if I had not evident knowledge of its being so; that is, carefully to avoid precipitancy and prejudice, and to embrace in my judgment only what presented itself to my mind so clearly and distinctly that I had no occasion to doubt it. The second, to divide each problem I examined into as many parts as was feasible, and as was requisite for its better solution. The third, to direct my thoughts in an orderly way; beginning with the simplest objects, those most apt to be known, and ascending little by little, in steps as it were, to the knowledge of the most complex; and establishing an order in thought even when the objects had no natural priority one to another. And the last, to make throughout such complete enumerations and such general surveys that I might be sure of leaving nothing out.
Discours de la M�hode. 1637."

De Morgan, Augustus (1806-1871)

"[When asked about his age.] I was x years old in the year x^2.
In H. Eves In Mathematical Circles, Boston: Prindle, Weber and Schmidt, 1969."