Newtonian telescope secondary mirror. This design reduces the size and cost of the telescope with a shorter overall telescope tube length (with the corrector extending the focal length in a "telephoto" type layout) combined with a less costly spherical mirror. Commercially produced versions of this design have been noted to be optically compromised due to the difficulty of producing a correctly shaped sub-aperture corrector in a telescope targeted at the inexpensive end of the telescope market. Newtonian telescope The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir
Galilean electromagnetism regroup and explain the somehow dynamic but non-relativistic quasistatic approximations of Maxwell's equations. In 1905 Einstein made use of the non-Galilean character of Maxwell's equations to develop his theory of special relativity. The special property embedded in Maxwell's equations is known as the Lorentz invariance. In Maxwell's equations frame, assuming that the speed of moving charges is small compared to the speed of light, it is possible to derive approximations that fulfill Galilean invariance. This approach enables the rigorous definition of two main mutually exclusive limits known as quasi-electrostatics (electrostatics with displacement currents or ohmic currents) and quasi-magnetostatics (magnetostatics with