noun (Physiol.) The art of measuring the duration of mental processes, or of determining the time relations of mental phenomena.

At first, says Professor Denton in his book, THE SOUL OF THINGS.
". . . the sensitive, or psychometer, is generally a merely passive spectator, like one who sits and observes a panorama; but in time he becomes able to influence the visions—to pass them along rapidly, or retain them longer for a close examination. Then the psychometer, at times, dwells in that past whose history seems to be contained in the specimen . . . [At last he] becomes released even from the specimen. At will he leaves the room, passes out into the air, looks down upon the city, sees the earth beneath him like a map, or, sailing still higher beholds the round world rolling into darkness or sunlight beneath him. He drops upon island or continent, watches the wild tribes of Africa, explores the desert interior of Australia, or solves the problem of the earth’s mysterious poles. He can do more than this: he becomes master of the ages,. At his command the past of island and continent come up like ghosts from the infinite night; and he sees what they were and how they were, what forms tenanted them, and marks their first human visitants; seeing the growth of a continent, and its fruitage in humanity, within the boundary of a little hour . . . the universe scarcely holds a secret that [the freed spirit] cannot behold with open eye.
The Psychometer, as we have remarked, does not have to be mesmerized for the exercise of the power. His eyes should be closed, the better to help concentration of thought upon the psychic observations. “Otherwise,” says Professor Denton,
. . . he appears to be in a perfectly normal condition during the time, and can readily notice what takes place in the room; frequently laying down the specimen, joining in the conversation, or drawing objects seen and then going on with the examination. When the specimen is in powder, it is merely necessary to stroke the forehead with as much as will cling to a damp finger; and where heavenly bodies are examined the rays are allowed to shine upon the forehead. [p. 33.]
For it is proved that not only are the images of the Past in “the fadeless picture galleries of the Akâ?a,” but also the sounds of past voices, even the perfumes of archaic flowers, withered ages ago, and the aromas of fruits that hung on trees when man was but a mumbling savage, and polar ice, a mile thick, covered what are now the fairest countries under the sun. [THE SOUL OF THINGS, HPB]