W. Watson wrote:
When I was a student (a very long time ago), I would sometimes buy
paperback books of many texts from Blackwells in England. The price was
usually about 1/2. Sometimes (back then, and maybe still), one could by
tech books from China that was on almost tissue paper pages. They were
quite cheap.

Here's another good book, "Optics", by Eugene Hecht, for $24, containing
the best treatment of superposition and interference that I have ever seen.

http://dogbert.abebooks.com/servlet/...805385665&x=46
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73, Cecil http://www.qsl.net/w5dxp