What The Indexes Cover:
The 3 "Indexes to Early American Periodicals" cover 3 separate time periods from 1741 to 1935 and are thought to include all known periodical publications that had their inception and ending during this time period. The actual periodicals are on microfilm in three microfilm collections of the same names (often referred to as APS I, APS II and APS III). Therefore, when searching the microfilm for a citation be sure to note the appropriate microfilm collection. The name of the microfilm collection is given on the final citation along with reel number and all other information needed to find a citation.
In some cases, your library may have originals of some of these periodicals and the indexes work equally well with the hard copy as the final citation will include the periodical title, volume and page numbers.