Here is a question about this article: From 1879, Watch Tower supporters gathered as autonomous congregations to study the Bible topically. Thirty congregations were founded, and during 1879 and 1880, Russell visited each to provide the format he recommended for conducting meetings. As congregations continued to form during Russell's ministry, they each remained self-administrative, functioning under the congregationalist style of church governance. In 1881, Zion's Watch Tower Tract Society was presided over by William Henry Conley, and in 1884, Charles Taze Russell incorporated the society as a non-profit business to distribute tracts and Bibles. By about 1900, Russell had organized thousands of part- and full-time colporteurs, and was appointing foreign missionaries and establishing branch offices. By the 1910s, Russell's organization maintained nearly a hundred "pilgrims," or traveling preachers. Russell engaged in significant global publishing efforts during his ministry, and by 1912, he was the most distributed Christian author in the United States.
What is the answer to this question: When did Russell visit each of the congregations to provide the format he recommended to conduct their meetings?
during 1879 and 1880