Encyclopaedia Britannica, 11th Edition, "Haller, Albrecht" to "Harmonium"

part in the genesis of the hallucination. This being so, we must be

content to leave the boundary between illusions and hallucinations ill-defined, and to regard as illusions _those false perceptions in which impressions made on the sense-organ play a leading part in determining the character of the percept_, and as hallucinations _those in which any such impression is lacking, or p...