The most
convenient method of observing the spot is by presenting to the eye in
not too rapid succession, blue and yellow glasses, or, still better,
allowing blue and yellow papers to revolve slowly before the eye. In
this way the spot is seen in the blue. It fades rapidly, but is
renewed every time the yellow comes in to relieve the effect of the
blue. By using a Nicol's prism along with this apparatus, the brushes
of Haidinger are well seen in connexion with the spot, and the fact of
the brushes being the spot analysed by polarized light becomes
evident. If we look steadily at an object behind a series of bright
bars which move in front of it, we shall see a curious bending of the
bars as they come up to the place of the yellow spot. The part which
comes over the spot seems to start in advance of the rest of the bar,
and this would seem to indicate a greater rapidity of sensation at the
yellow spot than in the surrounding retina. But I find the experiment
difficult, and I hope for better results from more accurate observers.
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