When we meet a fact which contradicts a prevailing theory, we must accept the fact and abandon the theory, even when the theory is supported by great names and generally accepted.

A discovery is generally an unforeseen relation not included in theory.

Men who believe too firmly in their theories, do not believe enough in the theories of others. So ... these despisers of their fellows ... make experiments only to destroy a theory, instead of to seek the truth.

First causes are outside the realm of science.

Man can learn nothing unless he proceeds from the known to the unknown.

The minds that rise and become really great are never self-satisfied, but still continue to strive.

Priestley [said] that each discovery we make shows us many others that should be made.