[Note to Psych Web Visitors: We have tried to make these documents readable with common web browsers by keeping the file length around 100,000 bytes or less. For chapters 5, 6 and 7 this required dividing the chapter into several segments, as you can tell by the location of links below. This book has been released in at least eight editions. The third edition, reproduced here, is old enough to be "public domain" (no longer restricted by copyright). More recent editions are available in bookstores.]