teacher to teach that which he does not know. Those teachers who are
strong enough should squarely refuse to do such work. This much-needed
reform is already beginning in our colleges, and I hope it will
continue. It is a relic of mediaeval times, this idea of professing
everything. When teachers begin to decline work which they cannot do
well, improvements begin to come in. If one will be a successful
teacher, he must firmly refuse work which he cannot do successfully.

It is a false idea to suppose that everybody is competent to learn or
to teach everything. Would our great artists have succeeded equally
well in Greek or calculus? A smattering of everything is worth little.
It is a fallacy to suppose that an encyclopaedic knowledge is
desirable. The mind is made strong, not through much learning, but by
the thorough possession of something.

Lay aside all conceit. Learn to read the book of nature for yourself.
Those who have succeeded best have followed for years some slim thread
which has once in a while broadened out and disclosed some treasure
worth a life-long search.

A man cannot be a professor of zoology on one day, and of chemistry on
the next, and do good work in both. As in a concert all are musicians
--one plays one instrument, and one another, but none all in perfection.

You cannot do without one specialty; you must have some base-line to
measure the work and attainments of others. For a general view of the
subject, study the history of the sciences. Broad knowledge of all
nature has been the possession of no naturalist except Humboldt, and
general relations constituted his specialty.