When Columbus had made the egg stand on an end all others could then do it.

When he had discovered America, every one said they might have done it also.

All great and important truths are simple, and when presented to the mind, although unknown before, seem as if they had been well known, there is such an accurate consistency between the mind and them.

This leads me to suppose that there is simple and useful truths in my volumes, as every one seems to take them for their own.

I can only say that they have cost _me_ many and many an hour of close observation, and deep and independent thinking.