[Illustration: Fig. 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.
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 the most 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).
[Illustration: Fig. 33. A diagram by Mr. E. Lee. (_Annals of Botany_, 1911, vol. 25.)]
A Diagram from the _Annals 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 the _Gills of Lamellibranchiata_ (Transactions of the Royal Society of London, B. vol. 195, 1903). The shading employed was either done by the draughtsman (at _ch_ and 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 are included 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's _Natural 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.