Books like The Principles of Psychology
Herbert Spencer
The Principles of Psychology is 381 pages, about 6 hours 59 minutes at 250 words a minute.
7 books to read next
How long each takes
Social Intelligence 7.4 h 
The Intelligence Trap 6.2 h 
Assessment of Children 14.5 h 
Are We Smart Enough to Know How Smart Animals Are? 6.4 h 
The Intelligence of Dogs 5.0 h 
Intelligence 6.8 h 
Maps of the Mind 4.1 h Bar height shows length. Estimated at 250 words a minute.