ERRATA.
The reader is requested to make the alterations enumerated below at once in order to prevent any misunderstanding.
On page 51, end of line 23, for “it” read “is.”
On page 66, line 15, for “Fig. 51” read “Fig. 52.”
On page 162, third line from bottom, for “n = b - 21” read “n = 21 - b.”
On page 163, line 7, for “n = 250 - 2 (250÷40)” read “n = - 250 - 2 (250÷40).”
On page 165, second line from bottom, for “G” read “E.”
On page 210, line 3, for “B” read “D.”
On page 212, end of last line, for “fallen” read “faller.”
On page 267, line 4, for “straps” read “shafts.”
The author is fully conscious of many shortcomings, which are inevitable in a task of this magnitude, but he believes that something has been done to formulate present knowledge and practice. Any suggestions of improvements or enlargements will be gratefully received, so as to enable future issues to be more valuable and useful.