A short, broad man of tremendous vitality, the physical type of Hereward, the last of the English, and his brother-in-arms, Winter, Sylvester’s capacious head was ever lost in the highest cloud-lands of pure mathematics. Often in the dead of night he would get his favorite pupil, that he might communicate the very last product of his creative thought. Everything he saw suggested to him something new in the higher algebra. This transmutation of everything into new mathematics was a revelation to those who knew him intimately. They began to do it themselves. His ease and fertility of invention proved a constant encouragement, while his contempt for provincial stupidities, such as the American hieroglyphics for π and e, which have even found their way into Webster’s Dictionary, made each young worker apply to himself the strictest tests.

De Morgan was explaining to an actuary what was the chance that a certain proportion of some group of people would at the end of a given time be alive; and quoted the actuarial formula, involving p [pi], which, in answer to a question, he explained stood for the ratio of the circumference of a circle to its diameter. His acquaintance, who had so far listened to the explanation with interest, interrupted him and exclaimed, “My dear friend, that must be a delusion, what can a circle have to do with the number of people alive at a given time?”

If pi wasn’t around, there would be no round pies!

It can be of no practical use to know that Pi is irrational, but if we can know, it surely would be intolerable not to know.

Once when lecturing to a class he [Lord Kelvin] used the word “mathematician,” and then interrupting himself asked his class: “Do you know what a mathematician is?” Stepping to the blackboard he wrote upon it:— [an integral expression equal to the square root of pi]
Then putting his finger on what he had written, he turned to his class and said: “A mathematician is one to whom that is as obvious as that twice two makes four is to you. Liouville was a mathematician.”

The Biblical value of pi, by comparison, is exactly three, as is clear from a verse in 1 Kings vii 23: 'and he made a molten sea, ten cubits from brim to brim, and his height was five cubit; and a line of thirty cubits did encompass him round about.'

This mysterious 3.141592..., which comes in at every door and window, and down every chimney.

What good your beautiful proof on [the transcendence of] π? Why investigate such problems, given that irrational numbers do not even exist?

[As a youth, fiddling in my home laboratory] I discovered a formula for the frequency of a resonant circuit which was 2π x sqrt(LC) where L is the inductance and C the capacitance of the circuit. And there was π, and where was the circle? … I still don’t quite know where that circle is, where that π comes from.