Punctuation and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed.

Simple typographical errors were corrected; occasional unbalanced quotation marks retained. Missing or incorrect accent marks in non-English words were not changed.

Ambiguous hyphens at the ends of lines were retained; occurrences of inconsistent hyphenation have not been changed.

Text uses both mid-level decimal points (·) and baseline decimal points (.) These have not been changed in this eBook.

Index not checked for proper alphabetization or correct page references.

Illustrations have been moved, when necessary, between paragraphs and outside of quoted material.

Pages with illustrations originally included the phrase, “To face page nnn”. Such phrases have been deleted in this eBook.

Captions for the three illustrations of ‘The Hawk’, on page 106, originally were below the last one, but are shown here below each one.

“Parseval-Siegsfeld” and “Parseval-Siegsfield” were printed that way, but both may be mis-spelled.

Page 160: In the sentence beginning “The travel of the centre of pressure”, the phrase “in the different tests) = 17 lbs.” was printed that way, with an unmatched right parenthesis.

Page 485: “on the other wise” was printed that way.