**Fig. 2-8.** The first six probability amplitudes
y_{n}(*x*)
for an electron moving on a line of length *L*. Note the y_{n}(*x*)
may be negative in sign for certain values of *x*. The y_{n}(*x*)
are squared to obtain the probability distrubrition functions *P*_{n}(*x*),
which are, therefore, positive for all values of *x*. Wherever y_{n}(*x*)
crosses the *x*-axis and changes sign, a node appears in the corresponding
*P*_{n}(*x*).