Inconsistencies in spelling, hyphenation, lay-out, the use of quote marks, diacriticals and accents, etc. have been retained.

Depending on the hard- and software used to read this document, some elements may not display as intended. The browser version of this document (available from www.gutenberg.org) gives best results, and contains larger versions of several illustrations.

The minor differences between the Table of Contents and the headings in the text have not been standardised.

Several plates have been printed with poor colour overlays, this has not been remedied.

Some double-page plates have been re-combined, but the area between the pages may not be exactly as printed in the original work.

Page 136, Professor Willis: should be Professor (William) Wallace; Professor (Robert) Willis invented other drawing tools.

Plate 26, pentagraph (2×): as printed in the source document.

Changes made:

Some missing punctuation has been added silently, some minor typographical errors have been corrected silently.

Some tables, calculations, formulas, etc. have been re-arranged for better readability.

Some of the illustrations and their captions have been rotated.

Page 15: apply a straight-edge F changed to apply a straight-edge D

Page 75, Fig. 75: Lehman’s Scale changed to Lehmann’s Scale

Page 83: the third reference line C D changed to the third reference line C A

Page 132: the erect manner and the reverse manner changed to the erect manner and the reverse manner.

Heading PLATES added after Index.