The Night-mare is commonly, and, I believe, justly, attributed to a stagnation of the Blood; but how this stagnation is produc’d, has not been explain’d, so far as I know, in a satisfactory manner. I have carefully collected the observations of the ancient Physicians concerning the prognostics of this Disorder; not for ostentation, but to shew at the same time the dangerous consequences and antiquity of it, in order to make those afflicted with it the more solicitous to remove its cause in the beginning; for it may be said of the Night-mare, as of many other Disorders, _Vires acquirit eundo_. Though the most temperate are sometimes afflicted with this Disease, yet experience shews that it is generally the offspring of excess: hence it must have been nearly _coeval_ with Bacchus (though it be omitted by the _Coan Oracle_;) and Homer probably alludes to its symptoms in the following lines: Ως δ’ εν ὀνείρω ὀυ δύναται Φευγοντα διωκειν Οὔτ’ αρ ὁ δύναται ὑποfευγειν, ὄυθ’ ὁ διωκειν. Iliad xxii. I have not introduc’d any thing in this Essay that did not appear serious or probable. I have therefore omitted an inquiry into the origin of many odd epithets and quaint names commonly given to this Disorder; such as _Hag-riding_, _Wizard-pressing_, _Mare-riding_, _Witch-dancing_, _&c._, nor did I think it requisite to mention particularly the _curious Charms_ adapted to each superstitious name. My aim has been to convey my sentiments with as much brevity and perspicuity as possible. If I have transgress’d this rule, in occasionally introducing some things known, in order to explain others, it was to be the more intelligible; I therefore hope, the more learned will excuse me. With pleasure I take this opportunity of acknowledging how much the hints I receiv’d from the instructive lectures of my ingenious Preceptor Mr. Monro, contributed to this undertaking. AN ESSAY ON THE Incubus, or Night-mare. CHAP. I. _Of the history and the various opinions concerning the cause of this Disorder._ In order to convey a distinct idea of the subject of the following pages, I shall, according to the old custom of medical authors, begin with the etymology of it. Altho’ we have reason to believe, as will afterwards appear, that this Disease was known long before the Greek language, yet, the earliest account we have of it, is from the Greek authors, who call’d it Εφιαλτης, and the Romans nam’d it Incubus, both which words partly express its effects. In our language it is generally known by the name of the NIGHT-MARE; which strange term probably arose from superstitious notions which the British had, and perhaps still have, of it. How it first obtain’d this odd appellation, I never could learn, nor is it material to know, since that name is sufficient to distinguish it from every other Disease.