But her solitary studies went also into heavier and less frequented paths. Dr. Carpenter had taught her to interest herself in mental and moral philosophy. She read about these subjects at first because he had written upon them, and afterwards because she found them really congenial to her mind. Locke and Hartley were the authors whom she studied most closely. Then the works of Priestley, and the study of his life and opinions--which she naturally undertook, because Dr. Priestley was the great apostle and martyr of Unitarianism--led her to make a very full acquaintance with the metaphysicians of the Scotch school. To how much purpose she thus read the best books then available, upon some of the highest topics that can engage the attention, soon became apparent when she began to write; but of this I must speak in due course later on. Two other of the most important events, or rather trains of events, in the history of her young womanhood, must be mentioned first. The earlier of these was the gradual oncoming and increase of her deafness. She began to be slightly deaf while she was at Mr. Perry's school, and the fact was there recognized so far as to cause her to be placed next to her teacher in the class. How keenly she even then felt this loss, she has in part revealed in the story of Hugh Procter; and a few lines from an essay of hers on Scott may here be added: "Few have any idea of the all-powerful influence which the sense of personal infirmity exerts over the mind of a child. If it were known, its apparent disproportionateness to other influences would, to the careless observer, appear absurd; to the thoughtful it would afford new lights respecting the conduct of educational discipline; it would also pierce the heart of many a parent who now believes that he knows all, and who feels so tender a regret for what he knows that even the sufferer wonders at its extent. But this is a species of suffering which can never obtain sufficient sympathy, because the sufferer himself is not aware, till he has made comparison of this with other pains, how light all others are in comparison." As pathetically, but more briefly, she says about herself:--"My deafness, when new, was the uppermost thing in my mind day and night."