To stay youthful, stay useful.
The excellency of every art is its intensity, capable of making all disagreeable evaporate.
The thought, the deadly thought of solitude.
All clean and comfortable I sit down to write.
Every mental pursuit takes its reality and worth from the ardour of the pursuer.
I find that I can have no enjoyment in the world but the continual drinking of knowledge. I find there is no worthy pursuit but the idea of doing some good for the world.