117. This illusion is best shown in the illustrations of the parallel lines that are crossed diagonally, with the result that the lines no longer look parallel because of the angles. Nevertheless, they are parallel, and the lines running diagonally at the bottom of this page are also parallel.
We present two practical illustrations of illusion in the use of lines. (See ¶ 112.) They represent the side-walls of two rooms of the same dimensions, but showing apparently different proportions, the perpendicular lines making the side-wall look higher and the horizontal lines making the side-wall look lower. (See page 59.)
[Illustration: Illustration B. (See ¶ 113.)]
The length of the wall space is shortened, moreover, by the perpendicular lines and lengthened by the horizontal lines.
118. No period expresses more clearly the joy of curves as opposed to the severity of straight lines than that voluptuous period of Louis XV known as Rococo. It was a profligate era, an era of pleasure, and the appended illustration of part of a frieze is in no way exaggerated, but a true example of a common expression. (See page 60.)
119. Distinct perpendicular lines give height effect, but they also narrow the apparent width of a wall space. It is best to have such line effects indistinct unless they appear as in the illustration on page 63, where they are intended to reduce the breadth effect of the pattern and neutralize a squat tendency.
Indistinct perpendiculars give height effect, and do not reduce the wall width.
[Illustration: Perpendicular lines, giving height effect.]
[Illustration: Perpendicular lines, giving height effect.]
120. In the study of color and its application authorities differ so materially that it is not only impossible to reconcile their theories, but the different terms used to express color thought create inextricable confusion.
121. One authority fixes the neutrals as being black, gray and white; another regards them as those hues or tones which lack definite color, like quaternaries. Authorities differ, moreover, upon even the fundamental principles. Chevreuil selects red, yellow and blue as the primaries; Dr. Thomas Young selects red, green and violet. Helmholtz selects carmine, pale green and blue-violet; Maxwell scarlet red, emerald green and blue-violet; Professor Rood agrees with Maxwell; Professor Church, of the Royal Academy of Arts, London, regards the primaries as red, green and blue; George Hurst, the English authority, fixes upon red, yellow and blue, the Brewsterian theory.