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
Differential geometry of curves space curves are only distinguished by the way in which they bend and twist. Quantitatively, this is measured by the differential-geometric invariants called the "curvature" and the "torsion" of a curve. The fundamental theorem of curves asserts that the knowledge of these invariants completely determines the curve. Let (i) formula_1, (ii) formula_2, and (iii) formula_3 be a non-empty interval of real numbers. Then a vector-valued function of class formula_5 (i.e., the component-functions of formula_6 are formula_7-times continuously differentiable) is called a parametric formula_5-curve or a formula_5-parametrization. Note that formula_10 is called the image of the parametric curve. It is important