There are now 3 versions of the harp of God available for download 2 have 1921 as date and 1 has 1928
The link is for 10 versions scanned by Google but only 3 are Full view and available for download
http://www.google.com/books?uid=852929969918013690 and search in labels for harp of god
or copy and paste the following link in order to go direct to the Harp of God listing
http://www.google.com/books?as_labels=the+harp+of+god&uid=852929969918013690&hl=e
searchwords to the left are leading to other downloads by Russell and Rutherford like What say the Scriptures about spiritualism?
If you are outside the US you may need a proxy server in the US to download
Also at the Archive is a different version of What say the Scriptures about spiritualism? : Proofs that it is demonism by Russell {in full color}
http://www.archive.org/download/whatsayscripture00russrich/whatsayscripture00russrich.pdf