Complex sentence: George Ripley and Charles A. Dana in editing the "American Cyclopædia", and from 1879 to 1880 with Sydney Howard Gay in the preparation of the last two volumes of his "History of the United States".
Split into simpler sentences: George Ripley and Charles A. Dana in editing the "American Cyclopædia". From 1879 to 1880, he was associated with Sydney Howard Gay in the preparation of the last two volumes of Gay's "History of the United States".