In his desire for a wider knowledge in the range of his profession, especially in the line of surgery, he visited Europe in the fall of 1841, spending the succeeding winter in visiting the hospitals of Paris, and in attending the lectures of the distinguished men who at that time had attained a position in medical science surpassing, in point of investigation and practical analysis, that of any other city. In the following spring he visited the principal cities of Italy, and for a while studied in the hospitals of London. On his return to Bradford he at once resumed the practice of his profession. He boldly and successfully attempted capital operations in surgery, and became the leading surgical operator and consulting physician for a large circuit. He fitted up a well appointed dissecting-room, and the advantages of his instruction were sought by many students, who can attest to the thoroughness of his teaching, especially in the department of surgical anatomy. His knowledge of technical anatomy was quite remarkable, and sometimes his students would contrive a plot to "stump" the "old doctor" by an intricate quizzing upon some obscure nerve or vessel. The attempt always proved futile; but the cunning students did not enjoy the fire of questions that followed from their teacher, who all too easily perceived the "soft impeachment." The term "old doctor" was applied by the students before their preceptor was thirty years old. In 1844, Dr. Cogswell was offered a professorship in the medical department of one of the leading colleges of New England, which he declined. He early manifested his interest in the elevation of the standard of medical practice, by suggesting to his professional brethren the importance of a local organization, and through his efforts the Essex North Medical Association was formed, composed of the leading physicians in the northern portion of the county. This society has had a vigorous growth, and is now merged into the Massachusetts Medical Society, under the title of the "Essex North District Medical Society." Although retired from active practice, he retains his membership in this society, and regularly attends the quarterly meetings, participating in the scientific and practical discussions, and manifesting a lively interest in the success of the younger members. Dr. Cogswell has been called upon to fill many positions of responsibility and trust; and since he retired from the active duties of professional life his whole time has been absorbed in the transaction of business of a public and private nature. He was elected president of the Union Bank in Haverhill, Mass., at its organization, in 1849, and was elected to the same office when that institution became the First National Bank, in 1864, which position he still retains. For many years he has been vice-president of the Haverhill Savings Bank, and was for a time a successful railroad president.