Date: 1734

"And perhaps it is owing to this Medium or Canal, among other things, that having two Eyes and two Ears we do not see nor hear double."

— Forbes of Pitsligo, Alexander Forbes, Lord (1678-1762)

Date: January 1739

"The vividness of the first conception diffuses itself along the relations, and is convey'd, as by so many pipes or canals, to every idea that has any communication with the primary one."

— Hume, David (1711-1776)

Date: January 1739

"The attention is on the stretch; the posture of the mind is uneasy; and the spirits being diverted from their natural course, are not governed in their movements by the same laws, at least not to the same degree, as when they flow in their usual channel."

— Hume, David (1711-1776)