Not so in the case of the internal region of mind.

The composite states of consciousness just described never remain perfectly uniform for the shortest conceivable duration.

They change continually, just as the contents of the kaleidoscope vary with every shake of the instrument.

Thus, one shade of feeling runs into another in such a way that it is often impossible to detect its exact quality; and even when the character of the feeling does not change, its intensity is undergoing alterations so that an accurate observation of its quantity is impracticable.

Also, in this unstable shifting internal scene features may appear for a duration too short to allow of close recognition.