How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service!

Letter to Henry Fawcett (Sept. 18, 1861) in Life of Henry Fawcett (1885) pp. 100-101, and in More Letters of Charles Darwin: a Record of his Work in a Series of hitherto Unpublished Letters (1903) Vol. 1, p. 195, ed., Sir Francis Darwin, Albert Charles Seward.