gards eyesight,
a savage who is accustomed to watch oxen grazing at a distance
becomes so familiar with their appearance and habits that he can
identify particular animals and draw conclusions as to what they are
doing with an accuracy that may seem to strangers to be wholly
dependent on exceptional acuteness of vision. A sailor has the
reputation of keen sight because he sees a distant coast when a
landsman cannot make it out; the fact being that the landsman
usually expects a different appearance to what he has really to look
for, such as a very minute and sharp outline instead of a large,
faint blur. In a short time a landsman becomes quite as quick as a
sailor, and in some test experiments[1] he was found on the average
to be distinctly the superior. It is not surprising that this should
be so, as sailors in vessels of moderate size have hardly ever the
practice of focussing their eyes sharply upon objects farther off
than the length of the vessel or the top of the mast, say at a
distance of fifty paces. The horizon itself as seen from the deck,
[4] and under the most favourable circumstances, is barely four
miles off, and there is no sharpness of outline in the intervening
waves. Besides this, the life of a sailor is very unhealthy, as
shown by his growing old prematurely, and his eyes must be much
tried by foul weather and salt spray.

[Footnote 4: Gould's _Military and Anthropological Statistics_, p.
530. New York, 1869.]

We inherit our language from barbarous ancestors, and it shows
traces of its origin in the imperfect ways by which grades of
difference admit of being expressed. Suppose a pedestrian is asked
whether the knapsack on his back feels heavy. He cannot find a reply
in two words that cover more varieties than (1) very heavy, (2)
rather heavy, (3) moderate, (4) rather light, (5) very light. I once
took considerable pains in the attempt to draw up verbal scales of
more than five orders of magnitude, using those expressions only
that every cultivated person would understand in the same sense; but
I did not succeed. A series that satisfied one person was not
interpreted in the same sense by another.

The general intention of this chapter has been to show that a
delicate power of sense discrimination is an attribute of a high race,
and that it has not the drawback of being necessarily associated
with nervous irritability.

SEQUENCE OF TEST WEIGHTS.

I will now describe an apparatus I have co