It is not unknown to you, that I have employed almost the whole of my Life in acquiring, or endeavouring to acquire, useful Knowledge by Study, Reflection, Observation, and by cultivating the Society of my Superiors in Intellect, both at Home and in foreign Countries. You know too, that at different Periods of my Life I have not only planned, but collected the materials for, many Works on various and important Subjects: so many indeed, that the Number of my unrealized Schemes, and the Mass of my miscellaneous Fragments, have often furnished my Friends with a Subject of Raillery, and sometimes of Regret and Reproof. Waiving the Mention of all private and accidental Hindrances, I am inclined to believe, that this Want of Perseverance has been produced in the Main by an Over-activity of Thought, modified by a constitutional Indolence, which made it more pleasant to me to continue acquiring, than to reduce what I had acquired to a regular Form. Add too, that almost daily throwing off my Notices or Reflections in desultory Fragments, I was still tempted onward by an increasing Sense of the Imperfection of my Knowledge, and by the Conviction, that, in Order fully to comprehend and develope any one Subject, it was necessary that I should make myself Master of some other, which again as regularly involved a third, and so on, with an ever-widening Horizon. Yet one Habit, formed during long Absences from those with whom I could converse with full Sympathy, has been of Advantage to me--that of daily noting down, in my Memorandum or Common-place Books, both Incidents and Observations; whatever had occurred to me from without, and all the Flux and Reflux of my Mind within itself. The Number of these Notices, and their Tendency, miscellaneous as they were, to one common End ("_quid sumus et quid futuri gignimur_," _what we are and what we are born to become; and thus from the End of our Being to deduce its proper Objects_) first encouraged me to undertake the Weekly Essay, of which you will consider this Letter as the Prospectus.