"I worked at this Essay in a very curious manner, which I have adopted in almost all my other works. I devoted to it the hours of the night when I was unable to sleep. I meditated in bed with my eyes shut, and turned and re-turned my periods in my head with incredible labour. Then, when I was finally satisfied with them, I stored them up in my memory until I was able to commit them to paper; but the time spent in getting up and dressing myself made me forget everything, and when I sat down in front of my paper I could recall scarcely anything of what I had composed."