The phenomenon whereby a sensation such as lightness, colour, or warmth tends to induce the opposite sensation in a stimulus that follows it. Successive warmth contrast can be demonstrated vividly by holding one's left hand in a bowl of cold water and one's right hand in a bowl of hot water for a minute and then transferring both hands to a bowl of lukewarm water, close to physiological zero; the lukewarm water feels hot to the left hand and cold to the right hand. This experiment was first alluded to somewhat obscurely in 1690 by the English philosopher John Locke (1632–1704) in his Essay Concerning Human Understanding (Book 2, Chapter 8, section 21), as an argument that some physical properties that can be sensed must be secondary rather than primary qualities, and in 1846 the experiment was described clearly and studied quantitatively by the German psychophysiologist Ernst Heinrich Weber (1795–1878). See colour contrast, contrast (2), lightness contrast, thermal adaptation, warmth contrast. Compare simultaneous contrast.