An author will naturally consider whether a photograph is to be reproduced by means of photogravure, collotype or half-tone. It is impossible to lay down any laws on the subject, but the following points should be considered.
If it is essential to have the reproduction in the text, a half-tone block must be used; it must, however, be remembered that the paper used for the letterpress may be very unsuited for the printing of half-tones. On the other hand, if it be immaterial where the picture is placed, then the relative merits of photogravure, collotype and kindred processes and half-tone must be weighed.
Provided that expense need not be considered, photogravure will, in the majority of cases, give the best results; on the other hand, if this process is too costly, then the choice lies between collotype and half-tone. The latter method will often give a result with more contrast as compared with collotype, whilst collotype will give a truer interpretation of the tones.
As has already been remarked, the best results with half-tone blocks only are to be obtained by the employment of a paper which seemingly has no lasting qualities; it therefore follows that if the reproduction forms an important record, the use of collotype is indicated, since many varieties of good paper are available. As a general rule photo-micrographs are best reproduced by collotype.
In order that the respective qualities of these three processes—photogravure, collotype and half-tone—may be compared, Plates 8, 9, and 10 have been made from the same photograph, a view taken by Dr. F. F. Blackman of the Bouche d'Erquy, a salt marsh in Brittany, which was selected chiefly on account of the large number of tones it contains.
Plate 8Plate 8.Photogravure
Plate 9Plate 9.Collotype
Plate 10Plate 10.Half Tone
These three plates are not entirely comparable, since the heavy shadows in the right hand bottom portion of the photogravure have been touched up by the engraver.This was not intended by the author, but the plate was retained as it shews that directions regarding this point should not be omitted when sending the drawing or photograph to be reproduced. It also indicates that for critical work, when an exact a facsimile as possible is required, collotype should be used, for the plate cannot be touched up.
With regard to the reproduction of drawings shaded by means of wash or pencil, the same remarks apply, with the addition that if it be possible to express what is desired by other means, suitable for reproduction by line block, these latter should be employed. To illustrate this point, Figures 5, 6, and Plate 11 have been inserted; all illustrate the vascular skeleton of a fern (Marattia fraxinea), the first one is in outline and the second is shaded by lines of varying thickness; both of these are reproduced by means of the line block, whilst the third is a reproduction by half-tone of a pencil-shaded drawing. In order to obtain a fair comparison, the half-tone is reproduced as a plate, owing to the fact that it would not print satisfactorily on the paper used for the letterpress.
Fig. 5Fig. 5
Fif. 6Fig. 6
Plate 11Plate 11
THE HALF-TONE THREE COLOUR PROCESS.—This process is much used for colour reproductions of various subjects; and, in view of the fact that the best results can only be obtained by the best photography, the object should, if possible, be sent to specialists for reproduction. In many cases, however, this is impossible,e.g., landscapes and animal and plant portraits amidst their natural surroundings, so that the scientist, if unable to make a water colour drawing, which will give by far the best result, must make his own negatives.
The first thing to do is to purchase a set of colour-filters, adapted to the colour-correct plates to be used, from firms who specialize in these matters, Messrs.Paget or Messrs. Wratten for instance, and from them the inexperienced should obtain full information regarding exposure, etc., for it is essential that the exposure of the negatives should be correlated in order that all may have the same tone-value.
The colour-screens, blue, green and orange, are made by dyeing gelatine with suitable stains; the films are stuck on to perfectly plane glass and are mounted in frames. In practice these screens are usually placed behind the lens, in which case a special camera is necessary, or they may be adapted to fit on to the front of the lens. In either case the procedure is the same; three negatives are taken one after the other through each colour filter, the exposure being modified in order that the tones in each case may be of equal value.
There are thus obtained three negatives which, of course, yield positives which look very different one from the other. These prints may be sent to the block makers, but it is better, on the whole, to send the negatives with clear indications as to the colour of each.
From each negative there is made by contact a transparency, and from these positives there are prepared a set of half-tone negatives from which are made the half-tone blocks.
The reproductions are made by superposed printing of the three blocks, yellow being printed first, then red, and finally blue (Plate 12).
Plate 12Plate 12.—Three Colour Half Tone.
As indicated above, it is hardly worth while to make negatives for this process unless the operator is a really skilful or at least an efficient photographer, and even then the final product may prove unsatisfactory.
Better results are generally to be obtained by sending to the block maker a Lumiere colour photograph with full instructions regarding any corrections in the colours which may be necessary.
Examples:—
Bateson:Mendel's Principles of Heredity, Cambridge, 1909. Church:Types of Floral Mechanism, Oxford, 1908. Seward:Darwin and Modern Science, Cambridge, 1909.
PHOTO-MECHANICAL LINE BLOCKS.—The photo-mechanical line block, commonly known as a zinco, is in a sense the lineal descendant of the wood block. As a means of reproduction the possibilities of line blocks are very great, for not only is it possible to reproduce by their means all kinds of line drawings, but also drawings in charcoal and crayon, provided they be suitably executed on a proper grained surface. In fact, an artist or draughtsman who has a thorough knowledge of the process and its capabilities can obtain extraordinary results. The process has the further advantage of being both quick and inexpensive, a few hours only being required to make the finished product.
Their mode of manufacture is the same in principle as for half-tone blocks; in the case of the latter, the method known as the enamel process was described; in the present instance a different procedure may be dealt with.
A photograph of the drawing is taken on a negative, the wet collodion process being generally followed, although dry process plates may be used.
A highly polished zinc plate is sensitised with bichromate of potash and gelatine, or by other means, and, when dry, is exposed under the negative.
The exposed metal plate is then taken into the dark room and evenly, but thinly, coated with etching ink. When the ink is dry, the plate is developed in water; the unexposed gelatine, and with it, the ink, will come away, its removal being helped by the judicious application of a dabber of wet cotton wool.
The plate may next be "rolled over" with an ink whichwill more stoutly resist the action of the acid than that used in the first inking, but prior to this it is usual to soak the plate in a mixture of gallic acid, phosphoric acid and gum. This second rolling up must be carried out as if the plate were for lithographic reproduction; and, when dry, powdered resin may be applied, in order to make a better acid-resist, as in the preparation of a lithographic stone.
The plate is now etched slightly in a weak solution of nitric acid; it is then rinsed, dabbed dry and placed upon a hot plate until the resin has stuck well to the ink. When cool, the margins, sides and back are protected from the action of the acid by means of a varnish and the plate is given its first real etch, which is a very slight one. After rinsing and drying, the plate is again heated until the ink and resin have melted and flowed down the exposed sides of the ridges of metal produced in the first etching. This application of ink and resin must be repeated in order that the exposed sides of the ridges may be well covered with the acid-resist and so will not be undercut. The plate is then given its second etch, and this is done with a stronger acid, after which the sides of the lines are again protected with resinous material in the same way as before. The third etch follows, after which the metal is thoroughly cleansed from all the ink, etc.
In order to smooth the shoulders of the lines, the plate is given a finishing etch: the cleaned plate is warmed and rolled up with hard etching ink; the metal is then heated until the ink becomes glazed, and, when cool, is placed in the acid bath for the requisite amount of time. If necessary the plate, after cleaning, is touched up with a graver, and the superfluous metal is cut away. Finally it is mounted on a block of wood, and after the corners and sides have been trimmed square, the block is ready for the press.
To illustrate the enormous improvement which may result from the block passing through the hands of a skilful engraver, two line blocks of a wood engraving by Riocreux (see p. 36) have been prepared. Fig. 7 is the impression given by the block as ordinarily turned out, whilst Fig. 8 is a precisely similar block which has been worked up by an engraver.
Fig. 7Fig. 7
Fig. 8Fig. 8
There are several other methods of making the blocks, but the principles are the same as in the foregoing process.
In examining the proofs it must be remembered that deletions are not the only alterations that can be made in the finished block; not only can lines be cut away, or their character altered by removing part of the metal from them, but additions can be made in reason. For instance, lines can be added across open spaces, and if part of the printing surface has been accidentally removed in cutting away the superfluous metal, the damage can be made good by building up with solder and working on this with the graver. If, however, the additions required are at all extensive or complicated, it is better to have a new block made.
Inasmuch as scientific illustrations are to describe and explain definite facts, the drawings must needs be materialistic rather than suggestive; in other words, a more or less conventional system must be employed.
In making their drawings for reproduction by line blocks, authors have at their disposal the black line, the white line, the black space, the white space, the black dot and the white dot, all of which may be combined in various ways. No tones, other than black and white, are available; if it be desired to represent half-tones, they must be rendered by the above-mentioned means.
In the majority of cases the originals should be made with black ink on white Bristol board or smooth white paper; ordinary lead pencil drawings on smooth paper are useless, and lead pencil, black crayon or charcoal in combinationwith grained paper or board should not be employed unless the draughtsman has the requisite skill and knows exactly the limitations of the line block. For all ordinary folk black ink and Bristol board cannot be improved upon.
The drawing may be made first with a soft lead pencil, using the camera lucida or other optical aids to correct delineation. The pencil lines are then gone over with ink; for this purpose a good black ink is necessary. Wolff's Indian ink, Higgins' waterproof ink and Steuber's waterproof drawing ink are highly satisfactory, and there are many others. With regard to pens, a suitable implement is all-important; Gillott's lithographic pens and Brandauer's No. 515 are recommended. For straight lines of an even thickness a ruling pen is very useful, and these may be obtained fitted with an adjustment which enables the worker to rule a line of a definite thickness,e.g., .5 mm. and so on.
All drawings should be made larger than it is intendedthe reproduction to be, for slight inaccuracies, ragged lines, and other blemishes will thus appear less obvious. This drawing on a large scale is often a stumbling block, because the work appears too open and the draughtsman is tempted to put in too much; this must be avoided, else the crowded lines may join together in the reduced reproduction. Also it must be remembered not to draw too finely, else the work in parts may disappear entirely in the reproduction. In drawing on an enlarged scale a certain amount of exaggeration may be employed, in order that when reduced the drawing may not be quite spiritless.
When representing a solid object, such as a plant or an animal, to shew the external morphology, it is to be borne in mind that form is the main thing to represent, and this can be expressed by outline drawing alone. In fact, more or less primitive methods must be employed, and better models cannot be followed than the best wood cuts.
Fig. 9Fig. 9. The Lesser Celandine (Ranunculus Ficaria).By R. G. Hatton. (From Hatton'sCraftsman's Handbook).
By R. G. Hatton. (From Hatton'sCraftsman's Handbook).
Fig. 10Fig. 10. The Lesser Celandine. After Fuchs.(From Hatton'sCraftsman's Handbook.)
(From Hatton'sCraftsman's Handbook.)
An examination of figures 10 and 12 will shew that Fuchs* attained his object by simple outline drawings; he never employed local colour, and shading he used very sparsely indeed, and then only to give expression to the form of some thick part. Fuchs's celandine (Fig. 10) should be compared with the drawing of the same plant (Fig. 9) by R. G. Hatton.
*The methods followed by the illustrators of the Herbals may be conveniently studied in Hatton's "The Craftsman's Plant Book," London, 1909, and Arber's "Herbals," Cambridge, 1912.
Fig. 11Fig. 11. The Apple (Pyrus Malus). After Matthiolus.(From Hatton'sCraftsman's Handbook).
(From Hatton'sCraftsman's Handbook).
The methods of Matthiolus (Figs. 11 and 13) were somewhat more advanced, for he used shading not only to express form but also to give a certain amount ofrelief. It will be noticed that he shaded by lines which followed the moulding of the parts.
The work of Riocreux (Fig. 8) should also be studied; it will be observed that he managed to get a very high relief in his drawings by the simple means of straight or curved lines, according to the shape of the part, of varying thicknesses.
Fig. 12Fig. 12. Charlock (Brassica Sinapis). After Fuchs.(From Hatton'sCraftsman's Handbook)
(From Hatton'sCraftsman's Handbook)
There is no necessity for keeping all the lines of even thickness. For instance, provided the character of the form is not altered, the outline on the shaded side maybe made thicker than on the illuminated side; also distance can be indicated by the use of thinner lines, for these, although really black, will give the impression of greyness. Then again, a line may be drawn with local increases and decreases in thickness, as in ordinary writing, and such lines drawn by a skilled hand can be made to express a marvellous amount of modelling.
Fig. 13Fig. 13. Sea Lavender (Statice Limonium). After Matthiolus.(From Hatton'sCraftsman's Handbook.)
(From Hatton'sCraftsman's Handbook.)
The draughtsman, however, is not restricted to lines; any marks which can be made with a pen and black ink may be employed, provided they be sufficiently firm and large.
The accompanying figure (14) which is a reduction of an illustration in Church'sFloral Mechanisms, illustrates the use of lines of varying lengths for shading.
Fig. 14Fig. 14.Viola odorata: Floral morphology.A reduction of a figure in Church'sFloral Mechanisms.
A reduction of a figure in Church'sFloral Mechanisms.
In shading, the effect of shadow may be obtained by increasing the thickness of the lines, but they must not be drawn too closely together; on the other hand, thelighter parts can be represented by thinner lines placed further and further apart, and the lightest parts by the white of the paper. Cross hatching may also be employed (see Fig. 15), but the crossed lines must not be too close together, for otherwise they will tend to thicken in the making of the block and so will print too black.
Fig. 15Fig. 15. A SeedlingofAbronia villosa.
For very delicate shading and tinting, stipple may be employed, but the dots must be quite definite, sufficiently large to stand reduction, and not too close together (Figs. 18, 28c, and 32). A particularly good example of this method will be found in Butler's paper onAllomycesin the Annals of Botany, 1911, vol. 25. Dots have also been employed in Fig. 28c (p. 69).
With regard to local colour; this may be indicated by shading, by a white space, or by a black space.
Hitherto, drawing with black ink on white paper alone has been considered, but the reverse is equally available; much can be expressed by drawing with white ink on black paper.
Drawing in white upon a black ground is not frequently attempted, but an excellent example by Miss Janet Robertson is shewn in figure 16, which is well worthy of study, since it illustrates to a nicety some of the means at the disposal of the draughtsman for line blocks. The black surface is best obtained by the use of a waterproof Indian ink applied with a brush to a white surface, the drawing being made with a dense white ink, using a pen or a brush. The white ink may be made by diluting any good opaque white water-colour paint, or process white may be used. The composition of this should be zincoxide or baryta, for these do not darken with age; the author once used for this purpose a white pigment which proved excellent at the time; the drawings, however, subsequently turned dark brown owing to the fact that the basis of the paint was apparently a compound of silver.
Fig.16Fig. 16.Neuropteris Heterophylla.A line reproduction of a drawing by Miss Janet Robertson.
A line reproduction of a drawing by Miss Janet Robertson.
The top part of the drawing (Fig. 16), shewing the general morphology of the plant, was drawn with a brush charged with white ink upon a black ground. In the simplest possible way relief has been obtained by representing the leaflets of the nearer fronds by white spaces, whilst those further away are represented by white outlines. An enlargement of a frond is shewn on the lower part of the picture, and here the parts are represented in black on a white ground. The leaflets are in black outline and the fruits are made to stand out, as in the upper part, by the use of local colour—in this instance black—their shape being indicated by the curve of the higher lights. In brief, a very effective drawing has been made by the simplest use of the white line, the white space, the black line and the black space.
Fig. 17Fig. 17.Fucus volubilis, var.Flexuosus, a seaweed.(From a drawing by Miss Baker.)
(From a drawing by Miss Baker.)
This may be compared with figure 17, which was drawn by Miss Baker; the method pursued is entirely different to the last, it being a pure pen and ink drawing on white paper. No local colour has been employed, and the modelling has been expressed by the lines used for shading which have been made by short strokes with a fine pen. The result is suggestive of an engraving but this was not intentional; under no circumstances should an attempt be made to imitate in a relief block effects which can only be obtained by intaglio.
From what has been said it is obvious that the photo-mechanical line block can be used for the reproduction of all kinds of drawings in pure black and white; to illustrate this figures 18-26 have been inserted.
Fig. 18Fig. 18. The Larkspur (Delphinium ajacis).By R. G. Hatton. (Hatton,Craftsman's Handbook.)
By R. G. Hatton. (Hatton,Craftsman's Handbook.)
Hollyhock (Althaea rosea).By R. G. Hatton.(Hatton,Craftsman's Handbook.)
A Seedling ofBruguiera gymnorhiza, a mangrove.Drawn by Mrs. F. E. Fritsch.(Tansley and Fritsch,New Phytologist, 1905, vol. 4.)
A Liverwort (Lepidozia reptans).(Evans,Annals of Botany,1912, vol. 26.)
Fig. 22Fig. 22A diagrammatic sketch by Mrs. F. E. Fritsch ofRhizophora conjugata, a mangrove.(Tansley and Fritsch,New Phytologist, 1905, vol. 4.)
A diagrammatic sketch by Mrs. F. E. Fritsch ofRhizophora conjugata, a mangrove.(Tansley and Fritsch,New Phytologist, 1905, vol. 4.)
Fig. 23Fig. 23A shoot ofAcanthus ilicifolia, a mangrove. Drawn by Mrs. F. E. Fritsch.(Tansley and Fritsch,New Phytologist, 1905, vol. 4.)
A shoot ofAcanthus ilicifolia, a mangrove. Drawn by Mrs. F. E. Fritsch.(Tansley and Fritsch,New Phytologist, 1905, vol. 4.)
Fig. 24Fig. 24A longitudinal section of a fossil seed,Conostoma oblongum.Drawn by Dr. E. J. Salisbury. (Oliver and Salisbury,Annals of Botany, 1911, vol. 25.)
A longitudinal section of a fossil seed,Conostoma oblongum.Drawn by Dr. E. J. Salisbury. (Oliver and Salisbury,Annals of Botany, 1911, vol. 25.)
Fig. 25Fig. 25The Meadowsweet (Spiraea ulmaria), shewing four years' growth. (Yapp,Annals of Botany, 1912, vol. 26.).
The Meadowsweet (Spiraea ulmaria), shewing four years' growth. (Yapp,Annals of Botany, 1912, vol. 26.).
Fig. 26Fig. 26. The Chesil Bank.(Oliver,New Phytologist, 1912, vol. 11.)
(Oliver,New Phytologist, 1912, vol. 11.)
Questions relating to the drawing of microscope sections may now be dealt with. Usually these are drawn in pencil and reproduced by means of lithography; this is quite wrong, for in addition to its being an unnecessary expense, it is also an inconvenience to a reader, since the figures are necessarily divorced from the letterpress. There are very few histological details which cannot be represented by line blocks, and with a proper co-operation between the author, the block maker, the printer and the publisher, even the delicacies of karyokinesis could be reproduced in the text.
For demonstration purposes, transverse sections of plant-structures may first be taken.
The walls of the various elements may be represented by lines of more or less equal breadth, but in those cases where the walls are particularly thick,e.g., the elements of the wood, the thickening may be represented by an additional line. This is seen in Fig. 27, in which it will be noticed that the middle lamellæ of the wood-elements are represented by black lines.
Fig. 27Fig. 27.(From Butler's paper on Gummosis ofPrunusandCitrus.Annals of Botany, 1911, Vol. 25).
(From Butler's paper on Gummosis ofPrunusandCitrus.Annals of Botany, 1911, Vol. 25).
This is a particularly good drawing, but, unfortunately, it has been over reduced.
On the other hand, the various tissues may be represented by lines of varying breadths, the thickest walled cells having the same double contour as in the above, but with the addition of local colour in the shape of diagonal shading. This is not uncommonly found in papers dealing with the anatomy of plants by French authors; it is illustrated in Figure 28a. If preferred, such thick-walledelements may be entirely represented by thick black lines as in Figure 28b, and when such cells are relatively few in number, this method has much to recommend it since a greater relief is obtained.
A transverse section to shewthe vascular cylinder of theroot of the spinach,cissomewhat older thanaandb.
Finally, an attempt may be made to draw in a more detailed fashion as in Figure 28c. Here the thickness of the cells of the wood is represented by broad black lines, the middle lamellæ being left white. The lines marking the boundaries of the other cells vary slightly in thickness, but this is to a great extent masked by the representation of the cell contents, which consist entirely of dots in the case of the protoplasm, whilst the nuclei are representedby dark ovals—black relieved with small white areas. By varying the size of the dots and their distance apart, varying densities can be indicated.
It has been mentioned above that it is possible to reproduce fine detail by means of the line block; this is illustrated in Figs. 29 and 30.
Fig. 29
Fig. 29, which illustrates a stage in the division of a nucleus, was drawn with black crayon on a rough-grained piece of Whatman's water-colour paper. The cytologist will, doubtless, criticize its coarseness, but it may be mentioned that the roughest paper at hand was designedly employed in order to illustrate the point raised. That a finer grained paper will give more delicate results is shewn by Fig. 30, which is a reproduction of a drawing, kindly lent by Dr. W. G. Ridewood, made with ordinary lead pencil on grained Bristol board. Its delicacy is obvious, and at first sight it could easily be mistaken for a lithograph.*
*Many similar examples will be found in Ridewood's memoirOn the Cranial Osteology of the Clupeoid Fishes, Proc. Zoo. Soc., Lond., 1904, vol. 11, p. 448.
Fig. 30
A half-tone can be put on to a line block during its manufacture. All that the draughtsman has to do, is to indicate by blue pencil lines those parts on which he requires the dots, which give the half-tone, to be placed, and to select the pattern of the stipple he desires to be used. The result may appear somewhat mechanical since the dots are regularly arranged, but a drawing sometimes may be considerably improved by this means if used with judgment. It is frequently employed in representing drapery, and many examples may be found on those pages of newspapers devoted to ladies' dress (Fig. 31; see also Fig. 32).
Fig. 31Fig. 31. After a water-colour design by Miss Winifred Pearse.
THE DRAWING OF DIAGRAMS AND APPARATUS.Much valuable information may be conveyed by diagrams; in fact, these could be used more freely than they are.
Fig. 32Fig. 32
The principles to be borne in mind are the same as for other ink drawings. They should always be drawn upon an enlarged scale, and with as little detail as possible, which generally should be indicated in themost conventional ways—dots, black spaces, lines, and so on (Figures 33 and 34). The main thing to be aimed at is clearness, so that it is often necessary to sacrifice true relative proportions in order to gain this end (Fig. 34).
Fig. 33Fig. 33. A diagram by Mr. E. Lee.(Annals of Botany, 1911, vol. 25.)
(Annals of Botany, 1911, vol. 25.)
Fig. 34Fig. 34A Diagram from theAnnals of Botany, 1912, Vol. 26.
A Diagram from theAnnals of Botany, 1912, Vol. 26.
In certain cases it is possible to combine detail and diagram in one drawing; this is shewn in Fig. 32, taken from Dr. Ridewood's admirably illustrated memoir on theGills of Lamellibranchiata(Transactions of the Royal Society of London, B. vol. 195, 1903). The shading employed was either done by the draughtsman (atchand in the cells with irregularly arranged dots), or else was put on the block during its manufacture (af). If a lens be used, the difference will at once be obvious.
The finished drawing should be bold and neat, and all lettering should be very clear. If several figures areincluded in one diagram they may be separated one from the other by ruled lines, and in no case should one tier of figures—taking the frames as the boundaries—unevenly overlap another tier, otherwise the diagram, to use an expressive phrase, will look "like a pig with one ear."
Under the heading of diagrams must be included the representation of apparatus. There are two ways of drawing apparatus; the objects may be drawn as a study in still life, as, for example, in many of the figures illustrating Deschanel'sNatural Philosophy(London, 1890) or they may be represented in a purely conventional fashion. The latter is the better way, and it is preferable to draw for the most part in section in order that all connections, inlets, outlets, etc., may be clearly shewn.
A study of a good example is infinitely better than a written description, wherefore Figure 35 has been inserted.
Fig. 35Fig. 35
It will be observed that all glass vessels and tubing are represented in section, and in the thermometers, the fine capillary bores are represented by a single line in each case; corks by diagonal shading; wood by lines in imitation of its grain; metal parts by vertical shading or dead black; more or less still liquids by a series of lines broken below and continuous at the surface, and gradually becoming closer and closer together towards the surface. Mercury, on the other hand, may be indicated by dead black relieved by a few white lines to represent its reflecting surface, also its free surface may be drawn convex. Finally thumb screws may be shewn by a combination of black areas and vertical shading.
These conventionalities need not all be followed; for instance, rubber connexions may be indicated by broad black lines and wood by diagonal shading.
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.
These three figures illustrate 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 36a), 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 36b) 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 100feet 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 36c). 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 associations.
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 compass or merely an arrow pointing to the north. Unless otherwise stated, the arrow is assumed 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 thevertical sides is a true north and south line, with the north at the top. Finally, under no circumstances 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).