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Mathematical Treasure: Consul the Educated Monkey

Sidney J. Kolpas (Delaware County Community College)

On June 27, 1916, the Educational Novelty Company of Dayton, Ohio, received US Patent 1,188,490 for “‘Consul’ The Educated Monkey”, a tin mathematical linkage toy. Consul was invented by National Cash Register draftsman William Henry Robertson, who previously was a secondary math teacher. According to the instructions accompanying the toy, the Educated Monkey was designed to

  • Teach the multiplication tables to 12s, associated elementary division, and associated elementary factoring.
  • Teach the addition tables to 12s, and associated elementary subtraction.

When the monkey’s feet are set to point at two numbers, its fingers locate their product. The image shows the left foot pointing to 4, the right foot pointing to 9, and the hands pointing to the product 36. To square a number, the monkey’s left foot is set to point to the number, and the right foot is set to point to the symbol of a square; the fingers then locate the square of the number. To divide, one foot is set to point to the divisor, and the fingers are arranged to point to the dividend. The other foot then points to the quotient. To factor, the fingers are made to point at a product, and the feet then point to the factors.  

Consul, the Educated Monkey, an early 20th-century mathematical toy.

“Consul,” the Educated Monkey, from the collection of Dr. Sid Kolpas.   

For addition/subtraction, the toy comes with a cardboard addition table that is slipped under the monkey. Addition and subtraction proceed in a manner similar to multiplication and division.

The instructions accompanying the toy indicate that it works due to the fact that the monkey is constructed around a plane mechanical linkage, and the products (sums) are arranged on the plate in a “special” order.  The linkage consists of 2 upper arm/leg pieces (which ensures that moving the feet to different factors forces the hands to move), 2 arm/hand pieces, and a tail with an answer window which moves up and down with different products (sums).  The 2 arm/hand pieces are attached to the tail, below the answer window.  The 2 upper arm/leg pieces are attached to the 2 arm/hand pieces at the “elbow” and also to the upper part of the tail (the head of a monkey is attached on top of this). Moreover, the feet on the upper arm/leg pieces slide along the straight line opening at the bottom of the toy's plate.

Six months before he filed this patent application, Robertson applied for a patent on a linkage intended to be used as a calculating device. US Patent 1,286,112 was also assigned to the Educational Novelty Company as soon as it was issued on November 26, 1918—Robertson served as president of the firm. Drawings from both patents are shown below. Unfortunately, the company was out of business by 1917. The Educational Toy Manufacturing Company of Springfield, Massachusetts, purchased rights to Consul and made the example pictured above.

Patent drawing for linkage by William H. Robertson, 1915. Patent drawing of educational mathematical calculating toy, Consul the Educated Monkey, 1915.

A simulation of Consul can be found at A Windows simulation can be downloaded at


Kidwell, Peggy Aldrich. Consul, the Educated Monkey, or the inventions of William H. Robertson. O Say Can You See? Stories from the Museum. National Museum of American History, 29 June 2015.

Kolpas, Sidney and Gary Massion. Consul, The Educated Monkey. Mathematics Teacher 93, no. 4 (April 2000).

Robertson, William H. Toy. US Patent 1,188,490, 27 June 1916.

Robertson, William H. Calculating Device. US Patent 1,286,112, 26 November 1918.

Wylie, Caitlin Donahue. What ‘Consul, the Educated Monkey’ Can Teach Us about Early-Twentieth-Century Mathematics, Learning, and Vaudeville. In The Whipple Museum of the History of Science: Objects and Investigations, to Celebrate the 75th Anniversary of R. S. Whipple’s Gift to the University of Cambridge, edited by Joshua Nall, Liba Taub, and Frances Willmoth, 237–256. Cambridge University Press, 2019. DOI: 10.1017/9781108633628.012.

Index to Mathematical Treasures

Sidney J. Kolpas (Delaware County Community College), "Mathematical Treasure: Consul the Educated Monkey," Convergence (December 2020)