Phrenology is a quirky pseudoscientific idea that personality traits can be "read" by feeling the shape of the bumps on the head.
The idea is that the brain controls the actual shape of the skull.
Everyone's skull is a bit bumpy, and phrenologists believed that the bumps were caused by more prominent traits of the brain physically pushing and shaping the skull.
The phrenologists developed a chart of the skull, dividing it into sections and defining which sections were supposedly related to which personality traits.
Thus, the phrenologist could then feel a person's skull and "read" the bumps on his head.
Cheap and plentiful pamphlets, as well as the growing popularity of scientific lectures as entertainment, also helped spread phrenology to the masses.
American brothers Lorenzo Niles Fowler (1811–1896) and Orson Squire Fowler (1809–1887) were the leading phrenologists of their time. Orson, together with associates Samuel Robert Wells and Nelson Sizer, ran the phrenological business and publishing house Fowlers & Wells in New York City.
Meanwhile, Lorenzo spent much of his life in England where he opened the famous phrenological publishing house, L.N Fowler & Co., and gained considerable fame with his phrenology head (a china head showing the phrenological faculties).
A replica of that head is in my collection...