Richard Clark wrote:
This specious argument (posing quadruple powers to confound
expectations) demands the slight of hand rhetoric ...

Do you really think that Born and Wolf engage in
"slight of hand rhetoric"? Quoting them speaking
of the combined intensity of two equal magnitude
waves, I1 and I2.

"... and the intensity varies between a maximum
value Imax = 4*I1, and a minimum value Imin = 0
(Fig. 7.1)."

Fig. 7.1 is a sinusoid with a varying amplitude
from 0 to 4*I1 on the Y axis and relative phase
angle plotted on the X axis.

The average intensity is, of course, 2*I1 in
accordance with the conservation of energy
principle. Such is the nature of constructive
and destructive interference.
--
73, Cecil http://www.w5dxp.com