bout
the accepted theory; for it tells us that so much less of the lighthouse
should be seen from the beach than from the Hoe, whereas less still was
seen. And many of the Plymouth folk went away from the Hoe that morning,
and from the second lecture, in which Parallax triumphantly quoted the
results of the observation, with the feeling which had been expressed
seven years before in the 'Leicester Advertiser,' that 'some of the most
important conclusions of modern astronomy had been seriously
invalidated.' If our books of astronomy, in referring to the effects of
the earth's curvature, had only been careful to point out how surveyors
and sailors and those who build lighthouses take into account the
modifying effects of atmospheric refraction, and how these effects have
long been known to vary with the temperature and pressure of the air,
this mischief would have been avoided. It would not be fair to say of
the persons misled on that occasion by Parallax that they deserved no
better; since the fault is not theirs as readers, but that of careless
or ill-informed writers.

Another experiment conducted by Parallax the same morning was creditable
to his ingenuity. Nothing better, perhaps, was ever devised to deceive
people, apparently by ocular evidence, into the belief that the earth is
flat--nor is there any clearer evidence of the largeness of the earth's
globe compared with our ordinary measures. On the Hoe, some ninety or a
hundred feet above the sea-level, he had a mirror suspended in a
vertical position facing the sea, and invited the bystanders to look in
that mirror at the sea-horizon. To all appearance the line of the
horizon corresponded exactly with the level of the eye-pupils of the
observer. Now, of course, when we look into a mirror whose surface is
exactly vertical, the line of sight to the eye-pupils of our image in
the mirror is exactly horizontal; whereas the line of sight from the
eyes to the image of the sea-horizon is depressed exactly as much as the
line from the eyes to the real sea-horizon. Here, then, seemed to be
proof positive that there is no depression of the sea-horizon; for the
horizontal line to the image of the eye-pupil seemed to coincide exactly
with the line to the image of the sea-horizon. It is not necessary to
suppose here that the mirror was wrongly adjusted, though the slightest
error of adjustment would affect the result either favourably or
unfavourably for Parallax's flat-earth th