The cultivation of science is a luxury of no common kind amid the bustle and vexation of life, and is quite compatible with the most active professional duties. Your education and the example you have had to copy will, I am sure, guard you against those presumptuous and skeptical opinions which scientific knowledge too often engenders. In the ardour of pursuit and under the intoxication of success scientific men are apt to forget that they are the instrument by which Providence is gradually revealing the wonders of creation, and that they ought to exercise their functions with the same humility as those who are engaged in unfolding the mysteries of His revealed will.

In a letter to James David Forbes, as found in Life and letters of James David Forbes, p. 39.