Inquiries into Human Facility and Its Development (1883), pp.66; Galton also noted (on p.66) that, in relation to the slide rule's markings, "the artist has not put in the divisions very correctly" (illustration at page 97, Plate II, Fig.34).]
Galton had conducted research ("Statistics of Mental Imagery", Mind, Vol.5, No.19, (July 1880), pp.301-318.) into the extent to which eminent scientists used "mental imagery". On the basis that Galton, himself, had a great personal ability to create, manipulate and employ vivid mental imagery, he was shocked to discover that most eminent scientists not only did not habitually employ mental imagery, but were also, generally, quite incapable of generating "mental images" at will (Galton, 1880). In order to supply a contrast, Galton cited the extraordinary case of Flinders Petrie -- who could easily manipulate precise technical equipment in the spaces of his own imagination.
Petrie, William Matthew Flinders; Quibell, J. E. (1895), "Naqada and Ballas. 1895", Six Temples at Thebes, Naqada and Ballas, Cambridge University Press, pp. 63–64, retrieved 10 October 2023
