Taken from pieces written for a periodical which he both founded and produced, it is normally published in two volumes: the first covering those articles published in the years 1873 and 1876, the second covering those published in the years 1877, 1880 and 1881.
Taken from articles he both authored and produced, it is typically published in two volumes: the first covering those pieces published in 1873 and 1876, the second covering those published in 1877, 1880, and 1881.