The propensity which leads an insane person to accomplish his purpose by burning, has been considered to merit particular notice, and to constitute a variety of monomania. Dr. Marc, of France, has published a memoir on the subject; he gives the name of pyromania to it, and considers that, like other insane propensities, it may be the result of instinct, or it may be the result of delusion--reasoning upon erroneous principles. [Alexander Morrison, M.D., "The Physiognomy of Mental Diseases," London, 1840]

An older word for it was incendiarism.