Astronomical Observatories 

 photographic. The results are studied and pre- 

 pared for publication in Pasadena, where the ad- 

 ministrative offices, measuring and computing 

 bureaus, the physical laboratory, and the extensive 

 shops for the manufacture of instruments are 

 located. 



A second departure from existing practice con- 

 sists in the manufacture of essentially all of the 

 instrumental equipment, except highly specialized 

 optical parts, and the more massive parts of 

 mountings, by the observatory itself. In this con- 

 nection we refer especially to the construction of 

 the great number of silver-on-glass mirrors with 

 diameters ranging from 100 inches down. 



A third departure from previous practice is the 

 provision made for the temporary emplojanent of 

 specialists from other institutions. 



The general plan of work at the Solar Observa- 

 tory is to carry on simultaneously observations 

 of solar phenomena, observations of the stars, and 

 investigations in the laboratory, and to co-ordinate 

 the results thus gained. By photographs taken di- 

 rectly and with the spectro-heliograph and spectro- 

 graph, it has been found possible to study not only 

 the surface features of the sun but also to penetrate 

 its atmosphere and to investigate its chemical com- 

 position and its physical condition at various 

 depths. 



It has been shown that a sun-spot is the center 

 of a local magnetic field and that it is probably an 

 electric vortex caused by the revolution of nega- 

 tively charged particles. There is a connection be- 

 tween the variations of terrestrial magnetism and 

 changes in the solar activity as indicated by the 

 flocculi. The intensities of the sun-spot fields are 

 too weak, however, to account for the magnetic 

 storms observed upon the earth. 



It has been proved that the sun itself is a magnet 

 whose poles are near the sun's poles of rotation, 

 and whose polarity — with reference to north and 

 south — agrees with the earth's polarity. 



The eff'ective relative levels in the sun's atmos- 

 phere of at least 27 chemical elements have been 

 determined, the element which occupies the high- 

 est level, so far as observed, being calcium, the next 

 hydrogen. In general the heavy elements occur in 

 the lower strata. The large scale of the solar image 

 has permitted 1200 bright lines in the chromo- 

 spheric spectrum to be photographed without an 

 eclipse, and it is found that their wave-lengths agree 

 well with those of corresponding dark lines in the 

 general solar spectrum. Great attention has also 



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