Immediately after entering Harvard, Dana showed a decided partiality for scientific pursuits. To Natural Philosophy, Natural History, and Chemistry, he mainly devoted his attention, making excursions into the surrounding country for the purpose of examining its geological structure, and collecting mineralogical and other specimens. The result of these rambles was embodied in a small volume, published in conjunction with his brother Dr. S. L. Dana, in 1819, entitled "Mineralogy and Geology of Boston and its Environs." While in college he formed, together with his brother and several classmates, a society for the cultivation of Natural Science and Philosophy, named at first for two distinguished French chemists, but afterward known as the Hermetic Society. Towards the close of his collegiate course he was appointed to assist Dr. Gorham, the professor of Chemistry, in preparing his experiments. That eminent physician and chemist soon became so much interested in the pupil who displayed such assiduity in scientific researches, that finding he intended to pursue the study of medicine, he kindly invited him to do so under his tuition. In 1813, Mr. Dana commenced his studies with Dr. Gorham, attending lectures at the Medical College, but though he became well acquainted with the principles and practice of the profession, he never relinquished his preference for Chemistry and Mineralogy. He became an active member of the Boston Linnæan Society, and the first paper read before it, entitled "An Analysis of the Incrustation formed upon the Basket of Eggs from Derbyshire, England" (presented by Judge Davis), was read by him. In the spring of 1813, the Corporation of Harvard College employed Mr. Dana to visit England in order to procure suitable apparatus for its chemical department. During his stay abroad he studied, for a time, under the instruction of the somewhat distinguished Frederic Accum. In consequence of this absence he did not receive his degree of M.D. till 1817, that of A. M. having been previously conferred. In the autumn of 1817, Dr. Dana was appointed to deliver a course of chemical lectures to the medical students of Dartmouth College. The professors in the Medical School were Dr. R. D. Mussey and Dr. Cyrus Perkins. These lectures were so satisfactory that the appointment was continued, and during the autumns of 1818, 1819, and 1820, he lectured at Dartmouth, residing during the intervals at Cambridge, where, in January, 1818, he was united in marriage with Matilda, third daughter of Samuel Webber, D.D., late president of Harvard College. In 1821, being appointed professor at Dartmouth, Dr. Dana removed to Hanover, where, relinquishing the practice of medicine, he devoted his whole attention to his favorite studies, to which was now added Botany, upon which he delivered some courses of lectures.