Keeler's "Photographs of nebulae and clusters ..."
reflector" is also available in scanned form from ADS, but the link
to the bibliographic data is done in a very bad form. One has to know
the titles of the chapters to find them inhttp://adsabs.harvard.edu/abstract_service.html -
only the first
chapter is given under Keeler's name.
Another way to access it is through
but this is also not very comfortable.
Both digitized versions have their advantages and disadvantages,
and both are not state-of-the-art. It is now possible to combine
in a PDF file both the scans (images of the pages) and the OCR
text, so that the user can see the original text and can also search
in the OCR'ed text. I may give links to examples if someone
Biography of former Allegheny Observatory Director James E. Keeler, whose remains are interred in the crypt below the Keeler Memorial Telescope at Allegheny Observatory, Pittsburgh: