An astronomer on an extended lecture tour became weary of delivering the same lecture night after night. He confided this state of mind to his chauffeur as they were driving to their next destination. The chauffeur expressed a similar boredom in his line of work.

Ive got it! said the astronomer. You are bored with driving and Im weary of lecturing. Lets exchange places for one night. It will be a refreshing change for both of us. My lecture is all written out word for word and nobody in the next town knows me by sight anyway.

The driver agreed and the exchange of roles and dress was made. That night the lecture hall filled to capacity. At the appointed time those in attendance heard a flawlessly delivered lecture. At its conclusion the lecturer basked in the euphoric applause. Then came the question and answer period.

Who discovered Uranus? came from a boy in the front.

Uh… William Herschel. He remembered that from somewhere.

And who discovered Pluto? continued the boy.

Aaaa… that would be Clyde Tombaugh. He had read a little.

Then from the back: Would you please comment on the relative merits of the pulsation instability model and the accretion disk instability model for the explanation of outbursts of cataclysmic variable stars?

The speaker paused for a moment and then said, I am surprised that you would bother to ask me such a simple question. And to show you how simple it really is, Ill have my chauffeur answer it for you.