The power or process by means of which Time is mentally recognised and estimated independently of, or before, its external and artificial measurement, has not received a clear or comprehensive solution at the hands of those who have dealt with the subject. Certain metaphysicians connect the idea of duration with that of extension, and conceive that the child, or the savage, may have acquired a notion of intervals, or interrupted extension, from seeing and feeling through the muscular sense the alternate extension and flexion of his limbs; all comparison of such events with the successive changes in objective phenomena, as in days and nights, being the result of subsequent experience. Certain others conceive that our notion of Time originates in our consciousness and observation of succession in our thoughts, feelings, and mental states, a succession which necessarily involves a series of changes separated in time, and order, and nature. Sir W. Hamilton, apparently aware of the difficulty of the problem, says that “Time is a form of thought,” and “if we attempt to comprehend Time, either in whole or in part, we find that thought is hedged in between two incomprehensibles.” Other philosophers, belonging to a more practical school, who may be claimed as psychologists, contend that the subjective element of Time is imparted by the communication of impressions upon the external senses to the sensorium, coming as these must always do in succession with intervals of different length, and, as they often do, of regular length and intensity. It will be observed that in all these hypotheses it is taken for granted that the mind is capable of directing attention to its own conditions, and, to a certain extent, of analysing these, of marking their course, their swiftness, or slowness, their regularity, or irregularity. On the other hand, the phrenologists contend that there is a primitive and special faculty connected with a portion of the anterior lobe of the brain, by which Time, or the succession of events and intervals, is perceived or becomes known to us. My own speculations formerly led me to the theory that the perception of rhythm, or regular sequence, in sensorial impressions was conveyed by the pulsations of the cerebral arteries, either to the whole brain, or to such portion of it as may take cognisance of internal movements or changes. Sir H. Holland, that noble veteran, that learned and travelled and philosophic physician, who has just passed from amongst us, dedicated a chapter in his “Medical Notes and Reflections,” p. 499, to the exposition of “Time as an element in Mental Functions,” in which his chief object is to show that ideas or different modes of mentalisation arise and are propagated in different degrees of velocity and intensity in Time in different temperaments, and in the same individual at different periods, in accordance with the predominant physical or mental condition.