sity, the appearance of
flickering results. That is what the cinematographer has to avoid. It
is found that a quicker succession--a shorter interval--is necessary
with strong light than with weaker light in order to produce
continuity. With a faint light the interval may be as great as
one-tenth of a second; with a strong light it must not exceed
one-thirtieth (or with still stronger light, one-sixtieth) of a
second. With the stronger light there is a more rapid and a greater
loss of the initial intensity of the impression or effect of stimulus,
and though each successive effect remains as long, or longer, in
dwindling intensity, you get want of continuity, or "flicker."]

[Footnote 4: What we may call the "visual size" of the sun happens to
be owing to its far greater size and its far greater distance from
us--very nearly the same as that of the moon--and is subject to the
same numerical law of apparent diameter, viz. a disc of any given
measurement in diameter will cover it exactly when held at a distance
from the eye which is 115 times that measurement.]

CHAPTER V

THE JEWEL IN THE TOAD'S HEAD

To what jewel or precious stone was Shakespeare alluding when he makes
the exiled Duke in "As You Like It" (after praising his rough life in
the forest of Arden, and declaring that adversity has its
compensations), exclaim:

"The toad, ugly and venomous,
Wears yet a precious jewel in his head"?

No doubt the unprejudiced reader supposes when he reads this passage
that there is some stone or stone-like body in the head of the toad
which has a special beauty, or else was believed to possess magical or
medicinal properties. And it is probable that Shakespeare himself did
suppose that such a stone existed. As a matter of fact there is no
stone or "jewel" of any kind in the head of the common toad nor of any
species of toad--common or rare. This is a simple and certain result
of the careful examination of the heads of innumerable toads, and is
not merely "common knowledge," but actually the last word of the
scientific expert. In these days of "nature study" writers familiar
with toads and frogs and kindred beasts have puzzled over
Shakespeare's words, and suggested that he was really referring to the
beautiful eyes of the toad, which are like gems in colour and
brilliance.

This, however, is not the case. Shakespeare himself was simply making
use of what was considered to be "common knowledge" in his day