The Connection betwixt our Ideas and the Motions excited in the Retina, Optic Nerves and Sensorium is unknown to us, and seems to depend entirely on the Will of God, who causes these Ideas or Sensations of which the Motions in the Sensorium are only the occasional Cause, . . . The Mind does not itself produce our Sensations, and consequently they must be produced either by God himself, or some subordinate active Intelligence, according as the Sensorium is moved by Objects. . . . Sensation must therefore be produced by some immaterial active Cause, and consequently either by the Mind itself, or by the power of God, or of some other intelligent active Being acting under him.
William Porterfield.
These are the musings of William Porterfield in an endeavor to comprehend the mysteries of the "Physiology of Vision," which no one yet had been able to solve for him, as he unreservedly set them