I've recently found that some important and obscure texts on knight's tours are now available in Google Books. The following are links to four of them:
Jaenisch's Treatise 1862
A problem with the Warnsdorf and Kafer books is that the Google versions do not reproduce the figures!
However I found a copy of the Kafer sheet of diagrams elsewhere on the web, and I was able to obtain a copy of the Warnsdorf tours through the kindness of Cleveland Public Library, Ohio.
More on this subsequently.
There are probably may other titles to be found by a search in Google Books.
Kafer details added in update of this page 1 Aug 2014.