The mere sense of light itself had increased eighteen
times. It was further noted that the sensitiveness to light rays,
after the eye had been rested, was developed in a special order; the
first color which was recognized being red, then followed yellow,
while green and blue respectively succeeded. If color fatigue was
produced in the eye by a glass of any special hue, it was found that
the color in question came last in the series in point of recognition.
The first of these experiments, regarded from a practical point of
view, would appear to consist in an appreciation of the revivifying
power of darkness as regards the sight. The color purple of the retina
is known to become redeveloped in darkness; and it is probable,
therefore, that the alternation of day and night is a physical and
external condition with which the sight of animals is perfectly in
accord.
* * * * *
SUN DIALS.
An article on the subject, recently published by us, has gained for us
the communication of two very interesting sun dials, which we shall
describe. The first, which we owe to the kindness of General Jancigny,
is of the type of the circular instrument, of which we explained the
method of using in our preceding article.
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