Principia Mathematica (vols. III)
(engl.)
at The University of Michigan Historical Mathematics Collection
[www.hti.umich.edu/cgi/t/text/text-idx?c=umhistmath;idno=AAT3201.0001.001]
[www.hti.umich.edu/cgi/t/text/text-idx?c=umhistmath;idno=AAT3201.0002.001]
[www.hti.umich.edu/cgi/t/text/text-idx?c=umhistmath;idno=AAT3201.0003.001]