To combat what precedes, the mental quality of the individuals composing a crowd must not be brought into consideration. This quality is without importance. From the moment that they form part of a crowd the learned man and the ignoramus are equally incapable of observation. This thesis may seem paradoxical. To demonstrate it beyond doubt it would be necessary to investigate a great number of historical facts, and several volumes would be insufficient for the purpose. Still, as I do not wish to leave the reader under the impression of unproved assertions, I shall give him some examples taken at hazard from the immense number of those that might be quoted. The following fact is one of the most typical, because chosen from among collective hallucinations of which a crowd is the victim, in which are to be found individuals of every kind, from the most ignorant to the most highly educated. It is related incidentally by Julian Felix, a naval lieutenant, in his book on "Sea Currents," and has been previously cited by the Revue Scientifique. The frigate, the Belle Poule, was cruising in the open sea for the purpose of finding the cruiser Le Berceau, from which she had been separated by a violent storm. It was broad daylight and in full sunshine. Suddenly the watch signalled a disabled vessel; the crew looked in the direction signalled, and every one, officers and sailors, clearly perceived a raft covered with men towed by boats which were displaying signals of distress. Yet this was nothing more than a collective hallucination. Admiral Desfosses lowered a boat to go to the rescue of the wrecked sailors. On nearing the object sighted, the sailors and officers on board the boat saw "masses of men in motion, stretching out their hands, and heard the dull and confused noise of a great number of voices." When the object was reached those in the boat found themselves simply and solely in the presence of a few branches of trees covered with leaves that had been swept out from the neighbouring coast. Before evidence so palpable the hallucination vanished. The mechanism of a collective hallucination of the kind we have explained is clearly seen at work in this example. On the one hand we have a crowd in a state of expectant attention, on the other a suggestion made by the watch signalling a disabled vessel at sea, a suggestion which, by a process of contagion, was accepted by all those present, both officers and sailors.