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An octahedron can be any polyhedron with eight faces. In a previous example, the regular octahedron has 6 vertices and 12 edges, the minimum for an octahedron; irregular octahedra may have as many as 12 vertices and 18 edges. [26] There are 257 topologically distinct convex octahedra, excluding mirror images. More specifically there are 2, 11 ...
Ørsted experiment (1820): Hans Christian Ørsted demonstrates the connection of electricity and magnetism by experiments involving a compass and electric circuits. Discovery of electromagnetic induction (1831): Michael Faraday discovers magnetic induction in an experiment with a closed ring of soft iron, with two windings of wire.
If two regular tetrahedra are given the same orientation on the 3-fold axis, a different compound is made, with D 3h, [3,2] symmetry, order 12.. Other orientations can be chosen as 2 tetrahedra within the compound of five tetrahedra and compound of ten tetrahedra the latter of which can be seen as a hexagrammic pyramid:
An object with this symmetry is characterized by the part of the object in the fundamental domain, for example the cube is given by z = 1, and the octahedron by x + y + z = 1 (or the corresponding inequalities, to get the solid instead of the surface). ax + by + cz = 1 gives a polyhedron with 48 faces, e.g. the disdyakis dodecahedron.
Pictet's experiment: Marc-Auguste Pictet: Demonstration Thermal radiation: 1797 Cavendish experiment: Henry Cavendish: Measurement Gravitational constant: 1799 Voltaic pile: Alessandro Volta: Demonstration First electric battery: 1803 Young's interference experiment: Thomas Young: Confirmation Wave theory of light: 1819 Arago spot experiment ...
The experiment became a popular way to illustrate the principles of air pressure, and many smaller copies of the hemispheres were made, and are used to this day in science classes. Reenactments of von Guericke's experiment of 1654 are performed in locations around the world by the Otto von Guericke Society.
Replacing each contact point between two spheres with an edge connecting the centers of the touching spheres produces tetrahedrons and octahedrons of equal edge lengths. The FCC arrangement produces the tetrahedral-octahedral honeycomb. The HCP arrangement produces the gyrated tetrahedral-octahedral honeycomb.
The tetrahedral-octahedral honeycomb, alternated cubic honeycomb is a quasiregular space-filling tessellation (or honeycomb) in Euclidean 3-space.It is composed of alternating regular octahedra and tetrahedra in a ratio of 1:2.