Denys Fisher Denys Fisher Denys Fisher (11 May 1918 – 17 September 2002) was an English engineer who invented the spirograph toy and created the company Denys Fisher Toys. He left Leeds University to join the family firm, Kingfisher (Lubrication) Ltd. In 1960 he left the firm to set up his own company, Denys Fisher Engineering, in Leeds. In 1961 the company won a contract with NATO to supply springs and precision components for its 20 mm cannon. Between 1962 and 1964 he developed various drawing machines from Meccano pieces, eventually producing a prototype Spirograph. Patented in 16 countries, it went on
Geometric calculus the correspondences of the differential form its derivative and its Hodge dual embed the theory of differential forms within geometric calculus. Following is a diagram summarizing the history of geometric calculus. Geometric calculus In mathematics, geometric calculus extends the geometric algebra to include differentiation and integration. The formalism is powerful and can be shown to encompass other mathematical theories including differential geometry and differential forms. With a geometric algebra given, let "a" and "b" be vectors and let "F(a)" be a multivector-valued function. The directional derivative of "F(a)" along "b" is defined as provided that the limit exists, where the