Transcriber's Notes:
Obvious printer's errors have been repaired, other inconsistent spellings have been kept, including inconsistent use of hyphen (e.g. "far reaching" and "far-reaching").
Some illustrations were relocated to correspond to their references in the text.
Pg. [816], word "of" added to sentence "...acceleration of social evolution."
Entries in Index refer to all five issues of Popular Science Monthly Vol. LV:
- May (pp. 1-136) http://www.gutenberg.org/ebooks/44880
- June (pp. 137-288) http://www.gutenberg.org/ebooks/45115
- July (pp. 289-432) http://www.gutenberg.org/ebooks/45361
- August (pp. 433-576) http://www.gutenberg.org/ebooks/45938
- September (pp. 577-720) http://www.gutenberg.org/ebooks/46383
- October (pp. 721-864), this issue.
Page number links have been created for index entries refering to the October issue.