At Hillingdon from Saturday till Monday last; began the Life of Mackintosh, and was delighted with Sydney Smith's letter which is prefixed to it; read and walked all day on Sunday--the two things I do least, viz. exercise my mind and body; therefore both grow gross and heavy. Shakespeare says fat paunches make lean pates, but this is taken from a Greek proverb. I admire this family of Cox's at Hillingdon, and after casting my eyes in every direction, and thinking much and often of the theory of happiness, I am convinced that it is principally to be found in contented mediocrity, accompanied with an equable temperament and warm though not excitable feelings. When I read such books as Mackintosh's Life, and see what other men have done, how they have read and thought, a sort of despair comes over me, a deep and bitter sensation of regret 'for time misspent and talents misapplied,' not the less bitter from being coupled with a hopelessness of remedial industry and of doing better things. Nor do I know that such men as these were happy; that they possessed sources of enjoyment inaccessible to less gifted minds is not to be doubted, but whether knowledge and conscious ability and superiority generally bring with them content of mind and the sunshine of self-satisfaction to the possessors is anything but certain. I wonder the inductive process has not been more systematically applied to the solution of this great philosophical problem, _what is happiness_, and _in what it consists_, for the practical purpose of directing the human mind into the right road for reaching this goal of all human wishes. Why are not innumerable instances collected, examined, analysed, and the results expanded, explained, and reasoned upon for the benefit and instruction of mankind? Who can tell but what these results may lead at last to some simple conclusions such as it requires no vast range of intellect to discover, no subtle philosophy to teach--conclusions mortifying to the pride and vanity of man, but calculated to mitigate the evils of life by softening mutual asperities, and by the establishment of the doctrine of _humility_, from which all charity, forbearance, toleration, and benevolence must flow as from their source? These simple conclusions may amount to no more than a simple maxim that happiness is to be found 'in the pursuit of truth and the practice of virtue.' Semita certe Tranquillæ per virtutem patet unica vitæ. The end of the tenth Satire of Juvenal (which is one of the finest sermons that ever was composed, and worth all the homilies of all the Fathers of the Church) teaches us what to pray for-- Orandum est ut sit mens sana in corpore sano.