The university president sighed as he went over the proposed budget offered him by the head of the department of physics.
“Why is it,” he said, mournfully, “that you physicists always require so much expensive equipment? Now the department of mathematics requires nothing of me but money for paper, pencils, and erasers.”
He thought a while longer and added, “And the department of philosophy is better still. It doesn’t even ask for erasers.”
Source: Asimov, The Humor Treasury.