Pysics and Astronomy

The Educated Monkey

The 'Educated Monkey' was patented in 1916 by W. H. Robertson. It is a toy 'for educational purposes ... to stimulate the interest of children in the study of numbers'.

sum product ass
                multiply You can add or multiply the two numbers.
Use the cross hair cursor and click to set a foot on a number.
Repeat to set the second number.
To set the same foot again, press command key to catch it, then release the key and click.
square     double
In product mode set the right foot on the square to read the squares of the numbers,
in sum mode set the right foot on 'D' to read the double of the numbers.
Check the box to reveal the geometric construction.

consul educated monkey construction

Mechanical Construction

The three distances of stud J to studs D, L, and E are equal each to each:

JD = JL = JE
and likewise:
KD = KL = KF

Hence the quadrangle JLKD is a rhomb.

The angle between the upper arm (red) and the leg (blue) is φ = 45° in my simulation. Then the triangle of the number table is including a right angle at its top.

A mathematical analysis (D. Haftendorn) proves that if the ratio of the distances is

ED/JD = 2*cos(45°) = sqrt(2)=1.41

the indicator for the result is moving along a straight line with slope m = 2*sin(45°)/sqrt(2) = 1 or 45°.

construction educated monkey
Web Links
Consul the Educated Monkey, or the inventions of William H. Robertson (P. A. Kidwell, Smithsonian)

William Henry Robertson's September 1915 patent for the educational novelty (PDF, Google Books)

Educated Monkey oder "Der rechnende Affe" (D. Haftendorn, Univ. Lüneburg)
Microsoft Word - educated-monkey.doc

2017  J. Giesen

updated: 2017, Feb 20