The Making of America project at Cornell University seems to be
nearing completion of its online journal collection and I thought it
might be of interest to many on this list.  It makes available (as
graphic scans of the pages) the complete contents of many of the
most influential American magazines of the 19th century, including
the Atlantic, Century, Galaxy, Harper's Monthly, North American
Review, Putnam's, Scribner's, etc.  Besides having many of Twain's
writings (starting with "Mark Swain's" Dec. 1866 debut in Harper's
with "Forty-Three Days in an Open Boat"), they are a great source
for the writings of others (Howells, Henry James, G. W. Cable,
etc., etc.) and for the general context of the times.  The collection
is not yet searchable but index pages are available for most
volumes.  The journals contents page is at

MOA Journal Collection
http://moa.cit.cornell.edu/MOA/Browsej.html

Jim Zwick