Correction:

Roy Lewallen wrote:
. . .
Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the left, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the left, and the sum is a horizontal field with magnitude equal to 2
fingers. . . .

My rotation was reversed -- it should read:

Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the *right*, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the *right*, and the sum is a horizontal field with magnitude equal to 2
fingers. . . .

The conclusion isn't affected by the error.

Roy Lewallen, W7EL