Opening the book…
9.1: Blimps, Balloons, and Models of the Atom is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.
The book could not be loaded just now.
Contents
Text
Size
From LibreTexts, under not declared, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.