Clark, 'Photography by Infrared' available online

I have found that the second edition of Walter Clark's 'Photography by Infrared' is available online through archive.org.

This is the only academic-style book on the subject. It was first published in 1939 with a second edition in 1946 and a third (revised by Henry Louis Gibson) in 1978. This last edition went out of print in 1984. Clark and Gibson both worked for Kodak, with Gibson having a particular interest in medical photography.

The electronic copy has very clear text and line diagrams but rather poor reproduction of photographs. However, this is the best source of background on the technique, with copious references for further study, and the second edition is IMHO the best of the three. Text is searchable.

Link to the various versions is: www.archive.org

[Update June 30 2011: the version now seems to be rights-protected]