Lines drawn down the forms give an appearance of great strength and toughness, a tense look.  And this quality is very useful in suggesting such things as joints and sinews, rocks, hard ground, or gnarled tree-trunks, &c.  In figure drawing it is an interesting quality to use sparingly, with the shading done on the across-the-form principle; and to suggest a difference of texture or a straining of the form.  Lines of shading drawn in every direction, crossing each other and resolving themselves into tone effects, suggest atmosphere and the absence of surface form.  This is more often used in the backgrounds of pen and ink work and is seldom necessary in pencil or chalk drawing, as they are more concerned with form than atmosphere.  Pen and ink is more often used for elaborate pictorial effects in illustration work, owing to the ease with which it can be reproduced and printed; and it is here that one more often finds this muddled quality of line spots being used to fill up interstices and make the tone even.

Speaking generally, #lines of shading drawn across the forms suggest softness, lines drawn in curves fulness of form, lines drawn down the forms hardness, and lines crossing in all directions so that only a mystery of tone results, atmosphere#.  And if these four qualities of line be used judiciously, a great deal of expressive power is added to your shading.  And, as will be explained in the next chapter, somewhat the same principle applies to the direction of the swing of the brush in painting.

Shading lines should never be drawn backwards and forwards from left to right (scribbled), except possibly where a mystery of shadow is wanted and the lines are being crossed in every direction; but never when lines are being used to express form.  They are not sufficiently under control, and also the little extra thickness that occurs at the turn is a nuisance.

The crossing of lines in shading gives a more opaque look.  This is useful to suggest the opaque appearance of the darker passage that occurs in that part of a shadow nearest the lights; and it is sometimes used in the half tones also.

Draughtsmen vary very much in their treatment of hair, and different qualities of hair require different treatment.  The particular beauty of it that belongs to point drawing is the swing and flow of its lines.  These are especially apparent in the lights.  In the shadows the flow of line often stops, to be replaced by a mystery of shadow.  So that a play of swinging lines alternating with shadow passages, drawn like all the other shadows with parallel lines not following the form, is often effective, and suggests the quality of hair in nature.  The swinging lines should vary in thickness along their course, getting darker as they pass certain parts, and gradating into lighter lines at other parts according to the effect desired. (See illustration, page 102 [Transcribers Note:  Plate XXI].)

[Illustration:  Plate XXI.