"To those who ask what the infinitely small quantity in mathematics is, we answer that it is actually zero. Hence there are not so many mysteries hidden in this concept as they are usually believed to be. These supposed mysteries have rendered the calculus of the infinitely small quite suspect to many people. Those doubts that remain we shall thoroughly remove in the following pages. "
"Madam, I have come from a country where people are hanged if they talk." [In Berlin, excusing his taciturnity in conversation with the Queen Mother of Prussia, on his return from Russia]