Rayleigh distance Rayleigh distance Rayleigh distance in optics is the axial distance from a radiating aperture to a point at which the path difference between the axial ray and an edge ray is λ / 4. An approximation of the Rayleigh Distance is formula_1, in which Z is the Rayleigh distance, D is the aperture of radiation, λ the wavelength. This approximation can be derived as follows. Consider a right angled triangle with sides adjacent formula_2, opposite formula_3and hypotenuse formula_4. According to Pythagorean theorem, formula_5. Rearranging, and simplifying formula_6 The constant termformula_7 can be neglected. In antenna applications, the Rayleigh distance is
What Is This Thing Called Love? What Is This Thing Called Love? "What Is This Thing Called Love?" is a 1929 popular song written by Cole Porter, for the musical "Wake Up and Dream". It was first performed by Elsie Carlisle in March 1929. The song has become a popular jazz standard and one of Porter's most often played compositions. "Wake Up and Dream" ran for 263 shows in London. The show was also noticed in New York, and the critics praised Tilly Losch's performance of the song. The show was produced on Broadway in December 1929; in the American rendition, "What Is This Thing Called