Even in the realm of things which do not claim actuality, and do not even claim possibility, there exist beyond dispute sets which are infinite.

My special pleasure in mathematics rested particularly on its purely speculative part.

Let me tell you how at one time the famous mathematician Euclid became a physician. It was during a vacation, which I spent in Prague as I most always did, when I was attacked by an illness never before experienced, which manifested itself in chilliness and painful weariness of the whole body. In order to ease my condition I took up Euclid's *Elements* and read for the first time his doctrine of *ratio*, which I found treated there in a manner entirely new to me. The ingenuity displayed in Euclid's presentation filled me with such vivid pleasure, that forthwith I felt as well as ever.