By Ye Shi-hui
Magnetism is likely one of the simple homes of subject. Mankind has trav elled a protracted highway in studying and using magnetism, and during this admire the traditional chinese language humans have made awesome contribu tions. within the e-book 'Lu's Spring and Autumn', written close to the top of the Warring States interval, i. e. within the 3rd century B. C. , there's a assertion at the "attraction of iron through lodestones". So at the moment it was once recognized that magnets can allure ferromagnetic fabric. on the be ginning ofthe first century A. D. , viz. within the early years ofthe East dangle Dynasty, the recognized pupil Wang Chong wrote in his masterpiece 'Len rooster' that the deal with of a magnetic dipper pointed to the south. It used to be therefore found on the time that magnets can aspect to the poles of the geomagnetic box. at first of the 12th century, in the course of the reign of Emperor Hui of the Sung Dynasty, within the books written by means of Zhu Yo and Xu Jin, respectively, there are descriptions of the com cross utilized in navigation. This tells us that the applying of compasses was once quite frequent at the moment. the celebrated scientist Sen cross (1031-1085) stumbled on the declination of the terrestrial magnetic box. this can be 400 and extra years just before its discovery through Christopher Columbus in 1492 in the course of his voyage around the Atlantic Ocean. Such evidence as those happen the real contributions of old China to international civilization.
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This is the same for the calculated B. In order to avoid this trouble, one may use lines which are weak in the photospheric spectrum but enhanced in the umbral one. 00 (Zwaan and Brants, 1981). Second, the magnetic field inside a spot may be different at various places. Generally speaking, by the magnetic field strength of a spot we mean its maximum strength. However, the atmospheric agitation and scattering cause the light rays from different parts of a spot to be mixed together, and so the measured B is less than the maximum value.
Optical scheme of photoelectric magnetograph. spots. D. W. Babcocks' invention of the photoelectric magnetograph (Babcock, 1953). This may be said to have revolutionized the observation of celestial magnetic fields, and this has led to a series of important discoveries. 1 FuNDAMENTAL IDEA Although the electronic circuits and mechanical structure of magnetographs may be quite complex, their basic principles are rather simple. Under the action of a weak magnetic field, the profiles ofthe two a components are close to each other.
CA) ~ ~ (") -e- ~ ..... ;:! ~ ~ ..... , CI) \::: ~ a..... 0-6).. " 1. -6>'. Fig. 2. Patterns of splitting in the longitudinal case (left) and transverse case (right). 1. ,2 as large as possible. The line with the longest wavelength ever used in spot magnetic observation, as far as we know, is Fe I ),,15649 (Rabin and Graves, 1989). ,2. One has still to consider its temperature sensitivity, blending with neighboring lines and some other factors. These questions will be discussed in the last section of this chapter.