Complex sentence: He was assistant editor of the "American Cyclopedia" from 1857 to 1863, which brought him to the attention of the literary editor of the "New York Tribune", George Ripley, who had him fill in for him temporarily while he was in Europe.
Split into simpler sentences: He was assistant editor of the "American Cyclopedia" from 1857 to 1863. This brought him to the attention of the literary editor of the "New York Tribune", George Ripley, who had him fill in for him temporarily while he was in Europe.