I was x years old in the year x2.

Lagrange, in one of the later years of his life, imagined that he had overcome the difficulty (of the parallel axiom). He went so far as to write a paper, which he took with him to the Institute, and began to read it. But in the first paragraph something struck him that he had not observed: he muttered: 'Il faut que j'y songe encore', and put the paper in his pocket.' [I must think about it again]

It was long before I got at the maxim, that in reading an old mathematician you will not read his riddle unless you plough with his heifer; you must see with his light, if you want to know how much he saw.

The sacred writings excepted, no Greek has been so much read and so variously translated as Euclid.

I don't quite hear what you say, but I beg to differ entirely with you.

But the gambling reasoner is incorrigible: if he would but take to squaring the circle, what a load of misery would be saved.

My opinion of mankind is founded upon the mournful fact that, so far as I can see, they find within themselves the means of believing in a thousand times as much as there is to believe in.