xhibited two horses in
Rome which could, upon request of their masters, point out those persons
among the spectators who were wearing stockings of any designated color.
The passage, "conoscevano i colori", (they recognized the colors,)
proves nothing and no one has ever heard, even in modern times, of a
horse that actually knew colors.

[Footnote W: All told, there are hardly more than half dozen
experimental investigations of the color-sense in mammals,--to speak
only of these. Three of them deserve especial mention. One, the work
of the American, Kinnaman,[33] on two Rhesus monkeys. Then a brief
but careful piece of work by Himstedt and Nagel.[34] These two
investigators were able to determine that their trained poodle could
distinguish red of any tone or shade from the other colors, and from
Professor Nagel I learned that later the tests were extended and the
same was shown to be true concerning the blue and the green. And
finally there is an investigation which hitherto has been known only
from a reference which Professor Dahl,[35] the investigator, himself
makes. The work is on a monkey, Cercopithecus (Chlorocebus)
griseoviridis Desm. (Professor Dahl has kindly allowed me to look
over the records of the experiments. He intends to publish the
monograph at an early date.)

All of these investigators arrive at the conclusion that the animals
tested by them possess color-sense. The monkey last-mentioned shows
one peculiarity: it was unable to distinguish a saturated blue from
the black. It will require further tests to clear this up.]

Nor did Hans possess anything like that high degree of visual acuity
which had been attributed to him. He was supposed to be able to read
easily at a distance small, almost illegible script, which we ourselves
could decipher only with the greatest difficulty close at hand. It was
also supposed that he could distinguish ten-and fifty-pfennig pieces
whose faces had become worn beyond recognition for us. None of these
accomplishments have stood the test. We have no reason to believe that
Hans can see the objects about him more clearly than other horses,
regarding whom one usually assumes that they receive only vague visual
impressions. Horses do not as a rule seem to be near-sighted as is often
asserted by the layman, but rather somewhat far-sighted, or if we may
believe Riegel,[37] who tested some six hundred hor