The first case is illustrated in the familiar example of taking a room to be brighter than it is when emerging from a dark one.

Another striking example is that of our sense of the temperature of objects, which is known to be strictly relative to a previous sensation, or more correctly to the momentary condition of the organ.

Yet, though every intelligent person knows this, the deeply rooted habit of making sensation the measure of objective quality asserts its sway, and frequently leads us into illusion.

The well-known experiment of first plunging one hand in cold water, the other in hot, and then dipping them both in tepid, is a startling example of this organized tendency.

For here we are strongly disposed to accept the palpable contradiction that the same water is at once warm and cool.
Far more important than these temporary fluctuations of sensibility are the permanent alterations.