I have just gone over my comet computations again, and it is humiliating to perceive how very little more I know than I did seven years ago when I first did this kind of work.

The best that can be said of my life so far is that it has been industrious, and the best that can be said of me is that I have not pretended to what I was not.

To read a book, to think it over, and to write out notes is a useful exercise; a book which will not repay some hard thought is not worth publishing.

There is no cosmetic for beauty like happiness.

Study as if you were going to live forever; live as if you were going to die tomorrow.

I am just learning to notice the different colors of the stars, and already begin to have a new enjoyment.