It was in this interval and by these means, that our young philosopher impaired his constitution, and contracted a pain in his breast; or rather, as he himself described that malady to the writer, “a constant heat in the pit of the stomach, affecting a space not exceeding the size of half a guinea, attended at times with much pain;” a sensation from which he was never exempt, during the remainder of his life. About this time, he retired from all business, and passed several weeks at the Yellow Springs, distant but a few miles from his place of residence. He there bathed and drank the waters; and from the use of this chalybeate, he appeared to have derived some benefit to his general health, though it afforded little alleviation of the pain in his breast. A due regard to the sacredness of historic truth demands, that some circumstances which occurred while Mr. Rittenhouse was yet a youth, and _one_ which it is believed had a very considerable influence on his subsequent pursuits and reputation, should now be made known. Because the writer of these memoirs conceives he ought not to be restrained, by motives which would appear to him to arise from a mistaken delicacy, from introducing into his work such notices of his own father, long since deceased, as do justice to his memory; while they also serve to elucidate the biographical history of Mr. Rittenhouse. In the year 1751, when David Rittenhouse was about nineteen years of age, THOMAS BARTON, who was two years elder than David, opened a school in the neighbourhood of Mr. Matthias Rittenhouse. It was while Mr. Barton continued in that place, supposed to have been about a year and a half, that he became acquainted with the Rittenhouse Family; an acquaintance which soon ripened into a warm friendship for young Mr. Rittenhouse, and a more tender attachment to his sister, Esther. Two years afterwards (in 1753), the personal attractions and fine understanding of the sister rendered her the wife of Mr. Barton; who, for some time before, had officiated as one of the tutors in the then recently-established Academy, afterwards College, of Philadelphia; now the University of Pennsylvania. In this station, he continued until the autumn of 1754; when he embarked for England, for the purpose of receiving episcopal ordination in the church, and returned to Pennsylvania in the early part of the following year. The very intimate connexion thus formed between Mr. Barton and a sister of Mr. Rittenhouse (who was two years elder than this brother), strengthened the bands of friendship which had so early united these young men: a friendship affectionate and sincere, and one which never ceased until Mr. Barton’s death, nearly thirty years afterwards; notwithstanding some difference of political opinions had arisen between these brothers-in-law, in the latter part of that period, in consequence of the declaration of the American independence.