This is a chapter from the excellent optics book "Seeing The Light"
(http://www.amazon.com/dp/0471603856), by Falk, Brill and Stork (Wiley, 1986)
It's a great resource for those starting to learn about the topic,
as it introduces the concepts very gently and in a layman-friendly manner.

Alas, I couldn't find any digital version online,
and I can't scan the whole book myself ΓÇö it's 450 pages long!
What I did, then, was scan the two chapters that I needed the most,
and thought it would be nice to at least make these two available for others.

This is the Wave Optics chapter. It contains 5 sections:
 1) Introduction
 2) Interference
 3) Applications of interference
 4) Babinet's and Huygens' principles
 5) Diffraction
At the end it has a summary, followed by a list of problems.

Here's a relevant passage from the introduction section:
  "Geometrical optics works when the relevant dimensions of the objects
  that interact with light (lenses, mirrors, stops, etc.)
  are much larger than lightΓÇÖs wavelength (about 1/2000 mm).
  To see wave phenomena, then, we must let light interact with tiny objects.
  Fortunately, the sizes needed are often not as small as the wavelength itself,
  but may be as big as a fraction of a millimeter.
  Indeed, weΓÇÖll see that using just your hands you can ΓÇ£squeezeΓÇ¥ a light beam
  to a sufficiently narrow width so it reveals its wave nature!"

I will provide the other chapter I scanned (Ch.14 - Holography) as a separate torrent. I'll put the link in the comments.

Below is the process and tools I used to make this "e-bookchapter";
this might be useful for others wanting to scan books for digital consumption.
All the tools I used are free and open source software
and can be found in the standard repositories of Ubuntu.

Step 1. Scanned the pages using simple-scan
Step 2. Processed using scantailor
Step 3. Cleaned up using gimp (removal of speckles, levels correction, removal of "shadows" from text and images the back of the pages, damage repair, and as a bonus, fix a typo: aranged --> arranged @ p.322)
Step 4. Merged the pages using imagemagick ("convert" command)
Step 5. Renumbered the pages using pdflatex, see http://askubuntu.com/a/34269
Step 6. Added metadata and bookmarks (table of contents) manually, using pdfmod

Note: I tried to perform OCR so the text would be searchable and selectable, but the results were quite bad and I decided to use only the raw images instead.