The moment I had read this, I seemed to behold another world, and became a different man.  Although I have a lively remembrance of the impression it made upon me, the detail has escaped my mind, since I communicated it to M. de Malesherbes in one of my four letters to him.  This is one of the singularities of my memory which merits to be remarked.  It serves me in proportion to my dependence upon it; the moment I have committed to paper that with which it was charged, it forsakes me, and I have no sooner written a thing than I had forgotten it entirely.  This singularity is the same with respect to music.  Before I learned the use of notes I knew a great number of songs; the moment I had made a sufficient progress to sing an air set to music, I could not recollect any one of them; and, at present, I much doubt whether I should be able entirely to go through one of those of which I was the most fond.  All I distinctly recollect upon this occasion is, that on my arrival at Vincennes, I was in an agitation which approached a delirium.  Diderot perceived it; I told him the cause, and read to him the prosopopoeia of Fabricius, written with a pencil under a tree.  He encouraged me to pursue my ideas, and to become a competitor for the premium.  I did so, and from that moment I was ruined.

All the rest of my misfortunes during my life were the inevitable effect of this moment of error.

My sentiments became elevated with the most inconceivable rapidity to the level of my ideas.  All my little passions were stifled by the enthusiasm of truth, liberty, and virtue; and, what is most astonishing, this effervescence continued in my mind upwards of five years, to as great a degree perhaps as it has ever done in that of any other man.  I composed the discourse in a very singular manner, and in that style which I have always followed in my other works.  I dedicated to it the hours of the night in which sleep deserted me, I meditated in my bed with my eyes closed, and in my mind turned over and over again my periods with incredible labor and care; the moment they were finished to my satisfaction, I deposited them in my memory, until I had an opportunity of committing them to paper; but the time of rising and putting on my clothes made me lose everything, and when I took up my pen I recollected but little of what I had composed.  I made Madam le Vasseur my secretary; I had lodged her with her daughter, and husband, nearer to myself; and she, to save me the expense of a servant, came every morning to make my fire, and to do such other little things as were necessary.  As soon as she arrived I dictated to her while in bed what I had composed in the night, and this method, which for a long time I observed, preserved me many things I should otherwise have forgotten.

As soon as the discourse was finished, I showed it to Diderot.  He was satisfied with the production, and pointed out some corrections he thought necessary to be made.