Origin and Psychological Cause of Laughter

This book deals with the cause and psychology of laughter.
“We laugh under the most diverse circumstances. Curious incidents of the most various character, some absurdly trifling and others rising into different degrees of importance, will provoke the feeling that prompts laughter, or the emotion of the ludicrous; for it is this with which we have to do, rather than with the audible explosion. Our inquiry is into the interior cause, into the moral element in the incident that provokes the feeling, and into what takes place in the nervous centers. The study of this is important, and has been well prosecuted by recent authors of the day, but the purely psychological element should not be neglected.
At the beginning of our inquiry we meet the common opinion that the feeling of laughter is caused by joy. This has the merit of simplicity; but joy does not always make us laugh, for there are serious joys; and we frequently laugh without being joyful, and even sometimes at things that are sad.”