The drawing should be very bold and the different parts clearly and freely indicated by writing or "printing."

THE DRAWING OF MAPS. In the drawing of maps for reproduction by the line block process, if an existing map serves the purpose, a tracing may be made in ink on translucent linen. If, on the other hand, the author has to make his own map, the problem becomes more difficult.

For the obtaining of the data for map making information must be sought for elsewhere, since we are only concerned in the preparation of the map for publication. And as regards this, but few general rules can be laid down since the character of maps is so diverse.

The amount of detail in the physical features represented depends to a great extent upon the scale. Thus streams of a greater breadth than, say, 10 feet, may in large scale maps be represented by double lines, whilst no stream less than 2 feet in breadth will be shewn in low scale maps.

[Ill.u.s.tration: Fig. 36

_a_ Contoured.

_b_ Spot-levels.

_c_ Layered.

These three figures ill.u.s.trate in three different ways the varying levels of a piece of ground surveyed by Prof. F. W. Oliver and Mr. A.

G. Tansley.]

The indication of hills is always a problem; the most satisfactory way is by the drawing of contours (Figure 36_a_), and this whenever possible should be followed, since it is scientifically the most correct method, inasmuch as when properly drawn the form of the hill is shewn exactly; further, contours obscure the detail to a much less extent than does shading, and but little artistic talent is required to draw them. If, however, contouring be impossible, the various heights above the datum may be shewn by spot levels (Figure 36_b_) or the relative levels may be shewn by layers; that is to say, by a system of shading each kind of which indicates a certain level. Thus dots may be used for all parts not more than 100 feet above sea level, vertical lines for regions between 100 and 200 feet, horizontal lines for parts between 200 and 300 feet, and so on (Figure 36_c_). It is obvious that this method cannot be pursued if vegetation also is to be shewn. The last choice is to represent the hill by shading in much the same way as many of us did when children; the method referred to was known as "herring bones" or "hairy caterpillars."

The sea or a broad expanse of water may be indicated by fine lines which follow the coast-line and which may be placed at gradually increasing distances apart.

If geological strata are to be represented, the accepted symbols should be used; if the map is intended to represent the distribution of soils, convenient signs may be employed, _e.g._, large dots for shingle or gravels, small dots for sand, black areas for clay, and so on; finally, if the distribution of plants or of animals is to be shewn, symbols again may be employed. These, however, must be quite simple and as far as possible give an idea of the organism represented. This, in the case of animals, may be a difficulty, but, with regard to plants, simple signs are easily inserted which give a very good idea of the plant it is intended to represent. Many of the signs used by the Ordnance Survey are ready to hand, and these can often be used to designate plant a.s.sociations.

The delimitation of areas should always be clearly shewn, and all names should be very clearly "printed" indeed, and if they must be placed on a dark portion of the map, they should have a good white border around them.

The north should always be indicated. This may be done by drawing in its proper position a representation of a compa.s.s or merely an arrow pointing to the north. Unless otherwise stated, the arrow is a.s.sumed to point to the magnetic north, and if no north be actually shewn it is taken for granted by an intelligent reader that one of the vertical sides is a true north and south line, with the north at the top.

Finally, under no circ.u.mstances should a scale be omitted--it is the first thing a reader should look for.

For a map to look well two things are all-important, neatness and clearness; both of these may nearly always be secured by drawing on a large scale, bearing in mind what has been said about crowding the detail, etc., and carefully considering how much reduction the original can stand. This last point is of vital importance, for an over-reduced map is an abomination; we have seen really good maps absolutely ruined by this stupid error.

The inexperienced author should study the methods pursued by Prof.

Yapp in Figure 37. For comparison, the simpler way adopted by Mr.

Wilson may be studied (_Annals of Botany_, 1911, Vol. 25).

[Ill.u.s.tration: Figure 37. A Map of the Fenland by Prof. Yapp. (_New Phytologist_, 1908, Vol. 7)]

GRAPHS OR CURVES. Simple though it be, the plotting of a curve for reproduction requires thought and care. In the first instance, the curve is drawn on squared paper, and the question naturally arises--To what extent are the squares to be represented? If it be desired to reproduce all the lines, say the paper is ruled in millimetres, a half-tone may be employed, or all these lines can be ruled over in black ink where the reproduction by line block is possible. It is, however, seldom necessary to represent all the smallest squares; it will generally be found that the centimetre squares are sufficient. If the original be plotted on paper which is ruled in pale blue, it can be reproduced by line block without re-drawing, since the blue will photograph as white with the plates commonly used; all the essential lines and curves must, of course, be in black. If, however, the rulings of the squared paper are in red, yellow, or dark blue, a tracing must be made. The horizontal and vertical sides should be ruled with a broad black line, but the internal intersecting lines should be much thinner. The actual curve may be in a continuous line if one only be shewn on the graph; if more are drawn, then each must be different, the obvious variations being the thick continuous line ---- the thin continuous line ----, dashes either thick or thin ---- ---- ----, dots . . . . . , and finally combinations of dots and dashes ---- . ---- . ---- .

Owing to the difficulty which some experience in drawing freehand a continuous line, the plot should be made twice the linear size of the intended reproduction. A good rule to follow in drawing lines is to keep the eye fixed on the point where the line is to end, the hand will then guide the pen in the right path, especially after a little practice. In many cases the ruler may be used, not only for straight but also for curved lines, for good curve rules may be purchased.

In order that the figure may look neat, the lines should be of an even thickness throughout their length; this is easily accomplished by means of a ruling pen.

It has been stated above that Bristol board is the best material to use for the making of drawings for line blocks; other materials may, however, be employed, although they are not so nice to work upon.

For instance, it may be necessary to reproduce a map; this, as has already been mentioned, may be conveniently done by pinning over the map a sheet of pale blue tracing linen, and tracing the map on this with Indian ink. The fact that the linen is blue does not matter, for it will photograph as if it were white.

Then again, many subjects may be of so complicated a nature as to be beyond the skill of the author to draw. In such a case a good plan is to take a photograph of the object and make a positive on smooth bromide paper, which need only be developed sufficiently far to give a print which just shows the features. The print, when dry, can then be worked on with fixed Indian ink. The finished drawing, when quite dry, may be immersed in any solution which will dissolve out the silver; a solution of iodine in pota.s.sium iodide answers sufficiently well. The print will turn very dark, but it must be allowed to remain in the bath until all the silver has dissolved; it is then removed, rinsed under the tap and placed in an ordinary fixing bath of hyposulphite of soda. All the colouration will be quickly removed so that the ink drawing will stand out well against the white paper. All that it now requires is a thorough washing in water; when dry it may be touched up and then placed under pressure in order to make it quite flat.[A]

[Footnote A: The chief disadvantage of iodine solution is its slowness of action; the following methods are much quicker.

(_a_) To a solution of 4 oz. of hyposulphite of soda in one pint of water, add a 10 per cent. aqueous solution of pota.s.sium ferricyanide until the mixture is lemon coloured.

When the silver image has quite disappeared, wash the print thoroughly in water. Since the mixture does not keep, the ferricyanide solution should be added to the hyposulphite solution immediately before use.

(_b_) Mix 125 ccs. of a 10 per cent. alcoholic solution of iodine with 21 ccs. of a 10 per cent. aqueous solution of pota.s.sium cyanide, add to the mixture 1 litre of water.

When the image has disappeared, which will be in less than a minute, wash for five minutes in water and dry.]

This method of drawing over photographic prints will often save a considerable amount of time. For instance, it may be desired to reproduce a consecutive series of drawings to ill.u.s.trate the microscopic structure of the subject. The ordinary way of doing this is to make camera lucida drawings of the sections, which is a lengthy and tiresome process; a photograph of each section will take much less time and will give quite as good results.

Before sending any line drawings to press they should be carefully examined; pencil marks may be rubbed out, lines touched up, unnecessary lines removed by painting them out with white or black ink according to the background, and, finally, a frame ruled around, if necessary.

The amount of reduction, which should be marked clearly on the margin, requires very careful consideration since under reduction may cause the reproduction to appear too coa.r.s.e whilst over-reduction may result in the loss of the finer detail and the drawing may, moreover, appear spiritless.

It must also be remembered that a reduction of, say, 1/2 linear means that the reproduction will be a quarter the area of the original.

The best way to indicate the reduction required is to draw a vertical or horizontal line, parallel to a side or the base of the picture, of the exact length; or, the line may be roughly drawn and its length indicated by figures thus ------------2-1/2"--------- .

The question arises as to when line drawings for reproduction by the zinc block should be employed.

The answer is, Whenever possible.

The advantages to a reader of having the ill.u.s.trations in the text has already been commented upon. It is about the only method commonly employed in which practically everything depends on the draughtsman; the author thus exercises the greatest control. Finally the fact that it is very inexpensive will appeal to editors and publishers.

As a matter of curiosity, the present writer picked out at random a recent volume of a scientific journal to examine the ill.u.s.trations; although there were a number of text figures, an examination of the plates--chiefly lithographs and collotypes--showed that there were a large number of figures which ought to have been in the text. A more detailed inspection of the plates was therefore made, with the result that nearly 200 figures were found which with the minimum amount of alteration--merely drawing in ink instead of pencil in the majority of cases, and leaving out unnecessary shading in the others--could have been reproduced by line blocks. If this had been done, a saving of over 20 per cent. could have been effected on the plates. Some of this would, of course, have been absorbed in the making of zincos, but not much, since line blocks of excellent quality can be obtained for 2-1/2d. and 3d. per square inch. The above relates only to the most obvious examples; the saving in plates would have been enormous if the authors had drawn for the line process.

THE SWELLED GELATINE PROCESS. From the foregoing account of the line-block it may, perhaps, be thought that a drawing shewing the finest detail cannot be reproduced in the text by a relief block made by photo-chemical means. This is not the case; the swelled gelatine process is such that at its best the very finest work can be so reproduced. The method is not extensively used, chiefly owing to the remarkable amount of skill required to produce the best results and to the facts that the blocks take longer to make and are more expensive than the ordinary line block. This, however, should not militate against its use, for the increased cost is but very little, and the longer time in making, say two days, should not be of any consequence in a monthly or quarterly periodical. The great point in its favour is its great fidelity as compared with the ordinary photo-chemical relief blocks: for instance, a close cross-hatching reproduced by a line block will often come out as a series of white dots owing to the fact that at the points of intersection the black lines tend to thicken; hence, on printing, the white s.p.a.ces, instead of being sharply cut and diamond-shaped, are rounded. This will not occur in a good block made by the swelled gelatine method. Further, the process does not restrict the draughtsman to dead black ink; the drawings may be made in pencil, crayon, or in ordinary writing ink: it is even claimed that wash drawings and photographs can be reproduced satisfactorily by this method. In the case of pencil drawings, the best results will be given when the surface of the paper used by the draughtsman is slightly rough; a pencil drawing on Bristol board, for example, will not be so well reproduced as one on ordinary smooth drawing paper. In brief, the process is as follows: a photographic negative of the drawing is made, and under it is exposed a bichromate gelatine plate. This plate is then developed in water. As already described, the gelatine will swell up in proportion to the amount of light to which it was exposed. The "positive" thus obtained will be in relief, the high lights being at a higher level than the shadows. A wax mould of the gelatine positive is then taken, covered with a thin layer of plumbago and electrically covered with copper. The "casting" so obtained is built up with metal and then mounted on wood in the same way as a zinco or a half-tone.

The capabilities of the process may be judged by a study of Fig. 38, which is an extremely faithful reproduction of a lithograph, by S.

Prout, by the swelled gelatine process.

[Ill.u.s.tration: Fig. 38. A Lithograph by S. Prout reproduced by the swelled gelatine process.]

[Ill.u.s.tration]

COST

RELATIVE COST OF BLOCKS AND PLATES