I have shown elsewhere, making use of certain physiological experiments, that the unconscious collective mind of the crowd seems bound up with the mind of the leader. The latter gives it a single will and imposes absolute obedience. The leader acts especially through suggestion. His success depends on his fashion of provoking this suggestion. Many experiments have shown to what point a collectivity may be subjected to suggestion.[6] [6] Among the numerous experiments made to prove this fact one of the most remarkable was performed on the pupils of his class by Professor Glosson and published in the Revue Scientifique for October 28, 1899. ``I prepared a bottle filled with distilled water carefully wrapped in cotton and packed in a box. After several other experiments I stated that I wished to measure the rapidity with which an odour would diffuse itself through the air, and asked those present to raise their hands the moment they perceived the odour. . . . I took out the bottle and poured the water on the cotton, turning my head away during the operation, then took up a stop-watch and awaited the result. . . . I explained that I was absolutely sure that no one present had ever smelt the odour of the chemical composition I had spilt. . . . At the end of fifteen seconds the majority of those in front had held up their hands, and in forty seconds the odour had reached the back of the hall by fairly regular waves. About three-quarters of those present declared that they perceived the odour. A larger number would doubtless have succumbed to suggestion, if at the end of a minute I had not been forced to stop the experiment, some of those in the front rows being unpleasantly affected by the odour, and wishing to leave the hall.'' According to the suggestions of the leaders, the multitude will be calm, furious, criminal, or heroic. These various suggestions may sometimes appear to present a rational aspect, but they will only appear to be reasonable. A crowd is in reality inaccessible to reason; the only ideas capable of influencing it will always be sentiments evoked in the form of images. The history of the Revolution shows on every page how easily the multitude follows the most contradictory impulses given by its different leaders. We see it applaud just as vigorously at the triumph of the Girondists, the Hebertists, the Dantonists, and the Terrorists as at their successive downfalls. One may be quite sure, also, that the crowd understood nothing of these events.