In the early 19th century, missionaries from across the United States travelled to mission fields around the world. Many of their letters and reports were collected and republished for the edification of those back home. One such publication in New England was the Panoplist, which later merged with the Massachusetts Missionary Magazine and eventually became the Missionary Herald. Listed below are links to scanned copies of these titles on the Internet Archive and Google Book Search.
For a look at how these titles fit into the larger succession of Congregational periodicals, take a look at this genealogical title map [PDF].
The Panoplist titles
Panoplist, or the Christian's Armory (1805-1808)
Panoplist and Missionary Magazine United (1808-1812)
Panoplist and Missionary Magazine (1812-1817)
The Panoplist, and Missionary Herald (1818-1820)