Gustave Le Bon 
The crowd a study of the popular mind [EPUB ebook] 

The Crowd: A Study of the Popular Mind, is a book authored by Gustave Le Bon that was first published in 1895.
In the book, Le Bon claims that there are several characteristics of crowd psychology: "impulsiveness, irritability, incapacity to reason, the absence of judgement of the critical spirit, the exaggeration of sentiments, and others…"
Le Bon claimed that "an individual immersed for some length of time in a crowd soon finds himself – either in consequence of magnetic influence given out by the crowd or from some other cause of which we are ignorant – in a special state, which much resembles the state of fascination in which the hypnotized individual finds himself in the hands of the hypnotizer.