Added to Online Library. Here is a book I was about to buy, until I found the entire text for free online. To copy Amazon's description:
One of the greatest and most influential books of social psychology ever written, brilliantly instructive on the general characteristics and mental unity of a crowd, its sentiments and morality, ideas, reasoning power, imagination, opinions and much more. A must-read volume for students of history, sociology, law and psychology.
It is about 200 pages. I haven't had the chance to read it yet, but it seems like a worthwhile book.