Final answer:
The author included photographs of first and third class staterooms to highlight the differences in accommodations and illustrate the class disparities of the time.
Step-by-step explanation:
The inclusion of photographs of first and third class staterooms is likely meant to show the differences between the first and third class accommodations. By contrasting images of the luxurious first-class saloons, such as the one on the Mississippi River steamboat Princess, with the cramped and poorly ventilated spaces of the steerage decks depicted in Stieglitz's photograph, 'The Steerage', the author highlights the stark disparities in living conditions and travel experiences on ships during that era. This comparison provides the reader with a visceral understanding of the class distinctions and social hierarchy that were prominent in the society of the time.