From 1840 to 1848, Long taught at the school for non-Christian students run by the CMS at its premises located on Amherst Street. Returning to India a married man in 1848, he was placed in charge of the CMS mission in Thakurpukur, at the time a hamlet a day’s journey out of Calcutta in the Bengal Presidency. By 1851, Long had set up a vernacular school for boys in Thakurpukur, while his wife Emily ran a corresponding school for girls. In an 1854 letter to F. J. Halliday of the Council of Education, he boasts a roll-call of "about 100 boys, Hindu, Mussulman, and Christians." His work "Bengali Proverbs" (1851) has been called a significant addition to Bengali literature. He studied Bengali proverbs and folk literature for another two decades, publishing "A Catalogue of Bengali Newspapers and Periodicals from 1818 to 1855" (1855), and the "Descriptive Catalogue of Vernacular Books and Pamphlets" which was forwarded by the Government of India to the Paris Exposition of 1867 .