photographic process more or less black, while either a red or blue
varying to a purple, will show more or less paint as the case may be."

As to deception which the eye will not detect, in regard to the age of
paper, he says:

"I have repeatedly examined papers which have been made to appear old
by various methods, such as washing with coffee, with tobacco, and by
being carried in the pocket, near the person, by being smoked or
partially burned, and in various other ways. I have in my possession a
paper which has passed the ordeal of many examinations by experts and
others, which purports to be two hundred years old, and to have been
saved from the Boston fire. The handwriting is a perfect fac-simile of
that of Thomas Addington, the town clerk of Boston, two hundred years
ago, and yet the paper is not over two years old."

The most remarkable case of deception to the eye, even when aided by
magnifying glasses, is in determining when two pen strokes cross each
other, which stroke was made first. Mr. Peacock does not explain how
the deception is possible, but that it occurs as matter of fact, he
shows by an account of a very decisive experiment. Taking ten
different kinds of ink, most commonly on sale, he drew lines on a
piece of paper in such a way as to produce a hundred points of
crossing and so that a line drawn with each of ink passed both over
and under all the lines drawn with the other inks. He, of course,
knew, in respect to each point of crossing, which ink was first
applied, but the appearance to the eye corresponded with the fact in
only forty-three cases. In thirty-seven cases the appearance was
contrary to the fact, and in the remaining cases the eye was unable to
come to any decision.