Letter 88 — On Liberal and Vocational Studies (§27)

“The wise man will know what causes the reflection in a mirror; but, the mathematician can merely tell you how far the body should be from the reflection, and what shape of mirror will produce a given reflection. The philosopher will demonstrate that the sun is a large body, while the astronomer will compute just how large, progressing in knowledge by his method of trial and experiment; but in order to progress, he must summon to his aid certain principles. No art, however, is sufficient unto itself, if the foundation upon which it rests depends upon mere favour.”