A mathematician, an engineer and a physicist sat around a table discussing how to measure the volume of a cow.

The mathematician suggested the use of geometry and symmetry relationships of the cow, but his idea was rejected on the grounds of being too time consuming.

The engineer suggested placing the cow in a pool of water and measuring the change in the height of the water, but his idea was rejected on the grounds of impracticality.

"It's easy," said the physicist. "We'll make an assumption that the cow is a small sphere, calculate the volume and then blow it up to the actual size."

If an engineer walks into a room and sees a fire in the middle and a bucket of water in the corner, he takes the bucket of water and pours it on the fire and puts it out.

If a physicist walks into a room and sees a fire in the middle and a bucket of water in the corner, he takes the bucket of water and pours it eloquently around the fire and lets the fire put itself out.

If a mathematician walks into a room and sees a fire in the middle and a bucket of water in the corner, he convinces himself there is a solution and leaves.

Physics professor has been doing an experiment, and has worked out an empirical equation that seems to explain his data. He asks the math professor to look at it.

A week later, the math professor says the equation is invalid. By then, the physics professor has used his equation to predict the results of further experiments, and he is getting excellent results, so he asks the math professor to look again. Another week goes by, and they meet again. The math professor tells the physics professor the equation does work, "But only in the trivial case where the numbers are real and positive."