"I certainly cannot have been born for study, for continuous application tires me to such an extent, that I am utterly unable to devote more than half an hour together to the close study of the same subject, especially when following another’s train of thought; for it has sometimes happened that I have been able to devote myself to my own ideas longer, and even with tolerable success. When I have read a few pages of an author who must be read carefully, my mind wanders from him, and is lost in the clouds. If I persist, I exhaust myself to no purpose; I become dazed, and cease to see anything. But if different subjects follow each other, even without interruption, one relieves me from the other, and, without feeling the need of any relaxation, I follow them more easily. I profited by this observation in my plan of study, and I combined them in such a manner that I was busy the whole day without ever fatiguing myself."