The department which includes the various time measurements in psychology is now called Mental Chronometry, the older term, Psychometry, being less used on account of its ambiguity.
III.

_An Optical Illusion._--In the sphere of vision many very interesting facts are constantly coming to light.

Sight is the most complex of the senses, the most easily deranged, and, withal, the most necessary to our normal existence.

The report of the following experimental study will have the greater utility, since, apart from any intrinsic novelty or importance the results may prove to have, it shows some of the general bearings of the facts of vision in relation to AEsthetics, to the theory of Illusions, and to the function of Judgment.
Illusion of the senses is due either to purely physiological causes or to the operation of the principle of Assimilation, which has already been remarked upon.

In the latter case it illustrates the fact that at any time there is a general disposition of the mind to look upon a thing under certain forms, patterns, etc., to which it has grown accustomed; and to do this it is led sometimes to distort what it sees or hears unconsciously to itself.