Titles for chapters and other parts of a manuscript usually begin on a new page. Use upper- and lowercase letters rather than full capitals. The titles should match the entries in the table of contents. “Chapter 1,” “Chapter 2,” and so on should appear above the titles to numbered chapters. (CMOS)
I’ve noticed that one Hallard publication used an arabic numeral to designate chapter numbers and another spells out the number. So is either way acceptable?
What good eyes you have, Roger!
According to CMOS:
Styling Numbered Chapters
Chapter numbers can be expressed in all kinds of ways.
1, 2, 3
I, II, III
Chapter 1, Chapter 2, Chapter 3
Chapter I, Chapter II, Chapter III
One, Two, Three
Chapter One, Chapter Two, Chapter Three
“Part numbers for a book are often numbered with roman numerals or spelled out simply to differentiate them from the arabic numerals used for chapter numbers. This organizational principle isn’t set in stone—there’s no rule against using arabic numerals for both part numbers and chapter numbers—but the differentiation that it provides can be helpful.”
I personally use roman numerals for sections of a book – Part I, Part II – and arabic for the chapter numbers- Chapter 1, Chapter 2.