[Illustration: Fig. 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. [Illustration: Fig. 36 _a_ Contoured. _b_ Spot-levels. _c_ Layered. 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.]