The manuscript was prepared by Dr. Clifford Earle from rough longhand notes
of the author. He has contributed many essential corrections, checked computations
and supplied many of the bridges that connect one fragment of thought with the
next. Without his devoted help the manuscript would never have attained readable
In keeping with the informal character of this little volume there is no index
and the references are very spotty, to say the least. The experts will know that
the history of the subject is one of slow evolution in which the authorship of ideas
cannot always be pinpointed.
The typing was excellently done by Mrs. Caroline W. Browne in Princeton, and
financed by Air Force Grant AFOSR-393-63.