is caused chiefly by the perspective lines of the drawing which force one to estimate relative height to a certain extent by the number of perspective lines intersected instead of by the actual size of the black pictures.
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Courtesy of the Grolier Society
Fig. 255. An Optical Illusion
The columns appear bent. The
left-hand pair seem closest
at the ends, while the right-hand
pair seem closest at
the center. The sides of the
columns are really straight
and parallel
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Courtesy of the Grolier Society and of Popular Mechanics
Fig. 256. An Optical Illusion
The policeman appears much taller than the
girl. In reality the figure of the girl is 1/16
inch taller than the figure of the policeman
Before charts are sent to an engraver to have plates made for printing it is wise to have each chart run the gauntlet of a series of questions, so that the time of the person doing the checking may be saved and also that the points more frequently overlooked may be thoroughly considered in each case. Below are given a series of questions which may be found convenient to anyone having charts to prepare. This list is not by any means complete, and the questions are given here as general suggestions only. The person checking a chart simply reads the questions one by one from the book, and then carefully observes the chart to see whether it comes up to the standard. Whenever possible it is well to have the chart checked by some person other than the one who drew it. In every editorial office the fact is recognized that one proof-reader will find important errors that were overlooked by another reader equally expert. Further, a mind much occupied with an idea may often fail to see important gaps in its statement, verbal or graphic, until perhaps they are noted by someone less familiar with the subject. Two points of view are always better than one.
