The whole internet collaborated to determine what this kitchen tool was.
The mixer with rotating parts was patented in 1856 by Baltimore, Maryland, tinner Ralph Collier.
This was followed by E.P. Griffith’s whisk patented in England in 1857. Another hand-turned rotary egg beater was patented by J.F. and E.P. Monroe in 1859 in the US.

Their egg beater patent was one of the earliest bought up by the Dover Stamping Company, whose Dover egg beaters became a classic American brand.
The term “Dover beater” was commonly in use in February 1929, as seen in this recipe from the Gazette newspaper of Cedar Rapids, IA, for “Hur-Mon Bavarian Cream,” a whipped dessert recipe featuring gelatin, whipped cream, banana and gingerale.