In most crude outdoor sketches the important features are usually shown with sufficient clearness to follow. If they are not the draftsman should ascertain what those features are and prepare the new drawing in such a way as to display them properly. The new drawing should be made with pen and ink, generally for reduction to a text figure, which is the most appropriate form for such an illustration. In all sketches of this kind the lines should be drawn in such a way as to produce natural effects and at the same time to make good printing plates. Good examples of pen and ink sketches of this class can be found in Monograph 34, already referred to, and in the Seventh Annual Report, especially Plates XXVIII and XXXVIII; Ninth Annual Report, Plates XLIII and XLIV; Tenth Annual Report, Plates XIV and XIX and figure 58; Eleventh Annual Report, Plates XV, XXVII, XXXV, LII, and LIV and figures 18, 30, 31, 67, 98, and 99. DRAWINGS OF CRYSTALS. A crystal should generally be drawn in outline with straight lines. The invisible rear side of a crystal, if shown, should be represented by dashed lines. The outer boundary line of a crystal should be slightly heavier than the inside lines, which should all be of the same weight. Striations should be shown by straight lines; broken or uneven surfaces by irregular lines. A twinning line, if an intersection edge, should be solid; if not an intersection edge it should be broken into dashes. Italic, Greek, German, and Old English letters are used to mark crystal faces. All faces of a given form should be marked by the same letter but may be differentiated, if necessary, by primes or numerals, thus: m, m', m'', m''', m{'v}. "Leaders" should be short full lines, or, if these are likely to be confusing, they should be dashes. Numbers may be used in place of letters for specific purposes. Letters indicating twin faces are underscored; a second twin is doubly underscored or overscored, thus: m_, m=, m¯. Twin units may be differentiated by the use of roman numerals. RETOUCHING PHOTOGRAPHS. An author, of course, selects his photographs to illustrate some special features; he does not always consider their fitness for reproduction. Photographs that are blurred or out of focus, those in which the shadows are too black or lack transparency, and those which have local defects, such as bad skies or spots, must be worked over to make them suitable for reproduction. In order to remedy these defects and produce natural results the draftsman doing work of this sort should be able to see and interpret nature properly and to supply natural effects in a manner corresponding with those produced photographically. He should be sufficiently expert with the brush and pencil and in handling an air brush to duplicate the delicate and soft tones in the photograph, and he should know how the pigments he uses will "take" when the subject is reproduced.