Page:Popular Science Monthly Volume 47.djvu/478

464 is broadened and the arches are apparently wider than is shown in Fig. 2.

In all these pictures the frame also is worthy of notice. In the first it has its true proportions; and in the second, it is distorted at the sides, and in the third, above and below.

There can be no question but that astigmatism even in a slight degree materially affects what the artist sees, and if it is true that he draws what he sees, does this not mean that his drawing tends to be proportionately faulty? Nor does it affect the vision for rectangular objects alone. This distortion is a constant quantity, and it does not take very exact study to see its effect in the drawing



of the figure. For this reason, often an undue plumpness is given to some portions, while others are rendered emaciated and anæmic to a degree of which the originals were never guilty.

Another disadvantage of astigmatism to the artists is that lines really parallel appear to converge or diverge, when distorted by the blurring which astigmatism can produce. The reason of this would require too great a digression here. The practical fact is that as the blurring is unequal when different parts of the objects are differently illuminated, and as the direction of the apparent blurs depends somewhat upon the form of the object, lines which should be straight have their direction apparently changed.