260 JOURNAL OF COSMETIC SCIENCE The distance between x and x' is 2r the area is •rr 2. q-rr 4 I31-- 4 --+ q'rr2 (2r)2 + -•-+ qxr2 (2r)2 - 4 P3 - 3q'rr 4 -- - 11.67 The distance between x and x' or x" is r or 3r the area is q'rr 2. I4/= 2(__•+•r4)+ 2(__•+9wr4 ) = 21,n. r4 P4/_ I4•/_21 P4 4q'rr 4 X n' th X n ! cross section, n is even the distance between x and X n is (n - 1)r.

DYNAMIC HAIRSPRAY ANALYSIS 261 I./=2-•-+•rr 4 +2 •-+9•rr 4 +...+2 +(n-1)2•rr 4 q'rr = 2 -•- + (2N- 1 )2 'rrr 4 1 -- 4 P n n'rr r REFERENCES (1) International Hair Science Symposium, Rostock, Germany, September 1996. (2) J.A. Swift, Some simple theoretical considerations on the bending stiffness of human hair, Int. J. Cosmet. Sci., 17, 245-253 (1995). (3) J. A. Swift, Letter to the Editor, J. Cosmet. Sci., 51, 37-38 (2000). (4) J. Jachowicz and K. Yao, Dynamic hairspray analysis. I. Instrumentation and preliminary results, J. Soc. Cosmet. Chem., 47, 73 (1996). (5) J. Jachowicz and K. Yao, Dynamic hairspray analysis. II. Effect of polymer, hair type, and solvent composition, J. Cosmet. Sci. 52, 281 (2001). (6) Den Hartog, Strength of Materials (Dover Publications, New York, 1977).