There are many people of narrow views, who greatly admire themselves, if once in a way, they have had a happy idea, or believe they have had one. An investigator, or an artist, who is continually having a great number of happy ideas, is undoubtedly a privileged being, and is recognised as a benefactor of humanity. But who can count or measure such mental flashes? Who can follow the hidden tracts by which conceptions are connected? That which man had never known, Or had not thought out, Through the labyrinth of mind Wanders in the night. I must say that those regions, in which we have not to rely on lucky accidents and ideas, have always been most agreeable to me, as fields of work. But, as I have often been in the unpleasant position of having to wait for lucky ideas, I have had some experience as to when and where they came to me, which will perhaps be useful to others. They often steal into the line of thought without their importance being at first understood; then afterwards some accidental circumstance shows how and under what conditions they have originated; they are present, otherwise, without our knowing whence they came. In other cases they occur suddenly, without exertion, like an inspiration. As far as my experience goes, they never came at the desk or to a tired brain. I have always so turned my problem about in all directions that I could see in my mind its turns and complications, and run through them freely without writing them down. But to reach that stage was not usually possible without long preliminary work. Then, after the fatigue from this had passed away, an hour of perfect bodily repose and quiet comfort was necessary before the good ideas came. They often came actually in the morning on waking, as expressed in Goethe’s words which I have quoted, and as Gauss also has remarked.[31] But, as I have stated in Heidelberg, they were usually apt to come when comfortably ascending woody hills in sunny weather. The smallest quantity of alcoholic drink seemed to frighten them away. [Footnote 31: Gauss, _Werke_, vol. v. p. 609. ‘The law of induction discovered Jan. 23, 1835, at 7 A.M., before rising.’] Such moments of fruitful thought were indeed very delightful, but not so the reverse, when the redeeming ideas did not come. For weeks or months I was gnawing at such a question until in my mind I was Like to a beast upon a barren heath Dragged in a circle by an evil spirit, While all around are pleasant pastures green. And, lastly, it was often a sharp attack of headache which released me from this strain, and set me free for other interests.