Fig. 30. A SHADING AND LETTERING CHART FOR DRAWINGS
The patent office has prepared a chart showing the shading that should be used to represent the different materials and colors and these are reproduced in Fig. 30. The letters of the alphabet both upper and lower case, as the capitals and little letters are called, which are used by mechanical draftsmen are also shown in Fig. 30. As these letters and figures are clear, easy to make and are preferred by the patent office they are good ones for you to use.
How to Make Electrical Symbols.—In making drawings, either for yourself or for the patent office, of electrical apparatus to show how it is connected up you do not need to draw out a plan view or a perspective of each part but you can make what are called symbols.
Symbols are simply a few lines or signs that stand for or represent a certain piece of apparatus; as an illustration suppose you want to show a dry cell, all you need to do is to make a couple of parallel lines, one shorter and heavier than the other like this:
and if you want to show a battery you make as many pairs of parallel lines as there are cells in this fashion:
And just so with every separate piece of electrical apparatus, and all of them are shown at A and B in Fig. 31.