The indulgence of the public has been already extended to several works which I have submitted to its decision on the subject of Insanity; and the same favourable interpretation is now solicited for the present performance, -which attempts the more difficult investigation of Sound Mind. In treating of Mental Derangement, I became very early sensible, that a competent knowledge of the faculties and operations of the Intellect in its healthy state, was indispensably necessary to him, who professed to describe its disorders: -that in order to define the aberrations, the standard should be fixed. There was indeed no lack of theories and systems of Metaphysic; and although they essentially differed, many possessed the highest reputation. Amidst this distraction of conflicting opinions, which no mediator could adequately reconcile, -without daring to contend with a host of discrepancies, or presuming to demolish the lofty edifices which scholastic Pneumatology had reared, -I determined to throw off the shackles of authority, and think for myself. For it was evident, on the freehold ground of literature, that there is "ample room and verge enough" for every man to build his own tenement;-and the present construction is too lowly to intercept another's prospect, and without those ornaments that might provoke the jealousy, or challenge the rivalship of surrounding inhabitants. The mind of every rational person may be considered as an elaboratory, wherein he may conduct psychological experiments: -he is enabled to analyze his own acquirement, -and if he be sufficiently attentive, he may note its formation and progress in his children: -and thus trace the accumulation of knowledge, from the dawn of infancy to the meridian of manhood. The prosecution of these means, according to my own views, will qualify the diligent observer, to become the Natural Historian and Physiologist of the Human Mind.