R. L. Fisher & S. Fisher 
Pretend the World Is Funny and Forever [PDF ebook] 
A Psychological Analysis of Comedians, Clowns, and Actors

First published in 1982. The intent of this book is to build an understanding of the people who create humor and are expert at making people laugh. Who are the comedians and clowns of the world? Where do they come from? Why are they so dedicated to tickling funny bones? In what ways are they unique? It is primarily to studying comedians, clowns, and other funny people. It seeks to provide an understanding of the origins, the motivations, and personalities of those who make humor and in exploring the factors that shape actors and other public entertainers.