http://www.archive.org/details/texts
The Internet Archive began life preserving snapshots of web sites and has evolved into a resources with a much broader focus. Often there are digitized books available for download that you won't find through Google Books or Hathi Trust. The search engine is a bit maddening, but the content is great.
Many early texts are now online, but navigating the databases in which they reside can be unwieldy.
Start with a subject bibliography, work off the bibliography of an overview article or secondary source, or refer to a compilation of documents as an easy - albeit indirect - entry into the material.
Connect to the campus network in order to access these databases.
Microfilm must be requested in advance from off-site storage [catalog location = Dartmouth Library Depository].
For more information contact me, or ask at the Berry Circulation Desk.
Collections of note (in roughly chronological order)