1. This chapter is almost entirely drawn from the material in the paper by M. Isaacson and M. Utlaut, Optik 50, 213 (1978).
2. M. L. Perlman, E. M. Rowe and R. E. Watson, Physics Today, July 1974, p. 30.
3. E. M. Rowe and J. H. Weaver, Sci. Amer. 236, 32 (1977).
4. J. Daniels, C. V. Festenberg, H. Raether and K. Zeppenfeld in Springer Tracts in Modern Physics 54 (1970) p. 78, ed. G. Hohler.
5. For an excellent overview of electron energy loss spectroscopy see D. C. Joy and D. M. Maher, Science 206, 162 (1979) .