(61) Davy pointed out the possible value of the gas as an anaesthetic in minor surgical operations, and now, long years after he did so, it has come into constant use for that purpose, particularly in dental surgery. It would not, I think, have been a far-etched speculation, if he had also suggested its possible value in states of mental depression, if inhaled in suitable doses, with a proper admixture of common air, and with sufficient frequency over a period of some length. That it can be inhaled with frequency and without injury his own experience proved. It went to prove even more, for he gives as its effects sound refreshing sleep, a good appetite, a sense of general well-being, and a healthy mental activity. If it led to anything like this in the case of a person under mental depression, might it not prove useful? The question at any rate is worth the asking. I am speaking of course of the inhalation of the gas as carried out by Davy, and not as now carried out to get anaesthesia in minor surgical operations. The pure gas is now used, and this does not appear to cause much if any exhilaration. To obtain this exhilaration it appears that the gas must be mixed with common air, and experiment could settle the desirable proportion of common air to nitrous oxide, and the quantity of such mixture needed to cause pleasant exhilaration only, without also causing boisterous laughter and gesticulations - a kind and degree of exhilaration, which those experiencing it would like to have prolonged and repeated.

(62) Dr. John Smith, LL.D., and Dr. Guy, two competent observers, tell me that they have neither heard nor known of any one who wished to inhale nitrous oxide solely from a desire to experience again the effects produced on a previous inhalation, when that inhalation had the production of anaesthesia as its object. But the gas as it is given for that purpose - they and others assure me - does not cause exhilaration, and this is attributed to its being inhaled in a pure state without any admixture of common air. The whole scheme of the apparatus

(65) There is a curious little book, published in Amsterdam in 1768, with the following title:-Traite des causes physiques et morales du Rire relativement a Part de lexciter. I believed it to be a scarce and little known book. It is anonymous, but it is attributed to Poiusinet de Sivri. He only claims, however, to be the editor of a manuscript which fell by accident into his hands. I have been in possession of a copy for many years, and I prepared an abridged translation, intending to give it as an appendix to this paper. But having recently obtained, from a quarter in which it was little likely to be found, a copy of a full and good translation into English, published in London (l2mo, 1769), I imagine that the book may not be so rare as I thought it, and that I would not, on the ground of its rarity, be justified in giving even an abridgment as an appendix to my paper. Therefore I have departed from my intention, and shall content myself with merely indicating the character of the book. The translator does not give his name. The somewhat changed title of the book runs as follows: - An Essay on Laughter, wherein are displayed its natural and moral causes, with the arts of exciting it. The translation is dedicated to Samuel Foote.

(66) The editor, Poinsinet de Sivri, says in his Avis that when the manuscript came into his possession it was simply entitled Traite du Rire, and he put it aside believing it to be a mere frolicsome performance, a light piece of drollery, a jev, d'esprit. But on the report of a friend who had borrowed the manuscript, he was induced to read it, found it to be replete with good ideas, and resolved to have it printed, it is called by the translator a learned and ingenious performance, and the original editor says that to all persons of taste the book must prove an agreeable present.

(67) The writer of the manuscript is of course made to appear as a different person from the editor. He says that the essay arose out of a visit by him to M. Titon du Tillet, where he met many men of distinction in letters and philosophy, among others, Destouches, Foutenelle, and Montesquieu. It happened that one of the company laughed without any apparent cause, and he was asked to tell why he had laughed, and was pressed to give an answer. He said that he would do so if others present would show what laughter is, and show also what excited them to laughter. Destouches, Foutenelle, and Montesquieu thought this a reasonable request, and they agreed to give the company their views, which they did after a stroll in the garden to gather up their thoughts. The writer of the manuscript says that it was his business to make a faithful recital of their opinions and arguments.

(68) Destouches was the first speaker, and with much elaboration and ingenuity he propounded and defended the view that laughter is the expression of a joyous and pleasant state of mind, with the very important qualification that the joy must be a reasoned joy,

(69) Fontenelle followed with an effort to overturn the opinions of Destouches, and then proceeded to show that all laughter represents in some way or other a state of mental disorder - enunciating his views with skill and earnestness.

(70) Montesquieu began by declaring, and attempting to prove, that the opinions of both of the speakers who preceded him were altogether erroneous, and he then endeavoured to show that laughter is born of pride and vanity - holding that he had completely established the soundness of that opinion.

(71) The foregoing is so brief and condensed a presentation of the three lines of thought that it must necessarily be imperfect, yet 1 think it sufficiently indicates the character of the differing views as to the nature and causes of laughter.

(72) The history of the book is obscure. The three orations may have been really delivered by Destouches, Fontenelle and Montesquieu. That is possible, for all three were in the prime of life from 1715 to 1745. They died, in the order in which I have named them, in the years 1754, 1757, and 1755 at the age of 74, 100, and 66. Titon du Tillet, in whose house they are said to have met, was also then alive. If the speeches were really made by these men, and at once committed to writing, the manuscript must have been somewhat old when it fell into the hands of Poinsinet de Sivri.