of nature is not wholly the same as that which man
sometimes calls truthfulness. It is far more imperious, far more exacting.
Man, unscientific man, is often content with the "nearly" and the
"almost." Nature never is. It is not her way to call the same two things
which differ, though the difference may be measured by less than a
thousandth of a milligramme or of a millimetre, or by any other like
standard of minuteness. And the man who, carrying the ways of the world
into the domain of science, thinks that he may treat nature's differences
in any other way than she treats them herself, will find that she resents
his conduct; if he, in carelessness or in disdain, overlooks the minute
difference which she holds out to him as a signet to guide him in his
search, the projecting tip, as it were, of some buried treasure, he is
bound to go astray, and the more strenuously he struggles on, the further
he will find himself from his true goal.

In the second place, he must be alert of mind. Nature is ever making signs
to us; she is ever whispering to us the beginnings of her secrets; the
scientific man must be ever on the watch, ready at once to lay hold of
nature's hint, however small; to listen to her whisper, however low.

In the third place, scientific inquiry, though it be preeminently an
intellectual effort, has need of the moral quality of courage--not so much
the courage which helps a man to face a sudden difficulty as the courage
of steadfast endurance. Almost every inquiry, certainly every prolonged
inquiry, sooner or later goes wrong. The path, at first so straight and
clear, grows crooked and gets blocked; the hope and enthusiasm, or even
the jaunty ease, with which the inquirer set out, leave him, and he falls
into a slough of despond. That is the critical moment calling for courage.
Struggling through the slough, he will find on the other side the wicket
gate opening up the real path; losing heart, he will turn back and add one
more stone to the great cairn of the unaccomplished.

But, I hear someone say, these qualities are not the peculiar attributes
of the man of science: they may be recognized as belonging to almost
everyone who has commanded or deserved success, whatever may have been his
walk of life. That is so. That is exactly what I desire to insist, that
the men of science have no peculiar virtues, no special powers. They are
ordinary men, their characters are common, even commonplace. Science, as
Huxley