Lord Macauley on Samuel Johnson's depression

A deep melancholy took possession of him, and gave a dark tinge to all his views of human nature and of human destiny. Such wretchedness as he endured has driven many men to shoot themselves or drown themselves. But he was under no temptation to commit suicide. He was sick of life; but he was afraid of death; and he shuddered at every sight or sound which reminded him of the inevitable hour. In religion he found but little comfort during his long and frequent fits of dejection; for his religion partook of his own character. The light from heaven shone on him indeed, but not in a direct line, or with its own pure splendour. The rays had to struggle through a disturbing medium; they reached him refracted, dulled and discoloured by the thick gloom which had settled on his soul, and, though they might be sufficiently clear to guide him, were too dim to cheer him.

Thomas Babington Macaulay, First Baron Macaulay, "Johnson, Samuel," Encyclopaedia Britannica, 8th ed., vol. 12, p. 794 (1856)

Part of this was quoted in A.J. Jacobs, The Know-It-All: One Man’s Humble Quest to Become the Smartest Person in the World (New York: Simon & Schuster Paperbacks, 2005), p. 81 (citing the 11th ed.).