Febeuabt 5, 1909] 



SCIENCB 



221 



explored, and reveal the existence of extensive 

 vortices or cyclonic storms associated with sun- 

 spots. In general, the direction of rotation of 

 the vortices is counter-clockwise in the north- 

 ern hemisphere and clockwise in the southern, 

 as in the case of terrestrial cyclones ; but a few 

 interesting exceptions, in which the direction 

 of rotation was reversed, have been found. 

 There can now be little doubt that what we 

 see in the telescope as a sun-spot is the mass 

 of vapor, cooled somewhat below the tempera- 

 ture of the photosphere, which lies at the 

 center of an invisible vortex {Astrophysical 

 Journal Vol. XXYHI., pp. 100-16). 



The discovery of these vortices suggested 

 that the rapid revolution of electrically charged 

 particles, emitted from carbon and other 

 vapors at the high temperature of the sun, 

 should produce a magnetic field in sun-spots. 

 Tests made with the 30-foot spectrograph of 

 the tower telescope show all the characteristic 

 phenomena of the Zeeman effect in the spot 

 spectrum, and leave no doubt as to the exist- 

 ence of a magnetic field. The strength of the 

 field has been found to range from about 2,800 

 to about 4,500 gausses in different spots. Vor- 

 tices rotating in opposite directions show op- 

 posite polarities, the changes in the spectrum 

 and in the polarization phenomena being pre- 

 cisely similar to those of a luminous source in 

 a magnetic field when the current through the 

 magnet is reversed. The results indicate that 

 the magnetic field is produced by the revolu- 

 tion of negative corpuscles in the vortices (see 

 Astrophysical Journal, Vol. XXVUI., pp. 315- 

 343). There is some evidence that the plane 

 of polarization of light passing through the 

 spot vapors is rotated through different angles 

 in different parts of the umbra, but more 

 observations of this phenomenon are needed. 

 For this and other purposes a tower telescope 

 160 feet high, giving a solar image 16 inches 

 in diameter, and a spectrograph Y5 feet long, 

 mounted in a well below the tower, should 

 prove of the greatest service. These instru- 

 ments are now being designed, and will soon 

 be constructed in our Pasadena shop.^ 



^ This telescope, of small aperture (12 inches) 

 and great focal length (150 feet), is designed 

 exclusively for work on the sun, where a large 



The above results are of some general in- 

 terest, since they conclusively demonstrate for 

 the first time the operation of electric phe- 

 nomena in the sun. So far as the cause and 

 nature of sun-spots are concerned, they seem 

 to favor Emden's theory. An attempt is now 

 being made to determine whether the sun as 

 a whole is a magnet. The tests already com- 

 pleted indicate that extremely sensitive meth- 

 ods will be required to settle the question, and 

 these will soon be applied. 



The 60-inch reflecting telescope, which has 

 been under construction in our instrument and 

 optical shops during the last four years, is now 

 in operation on Mount Wilson. Visual and 

 photographic tests show this instrument to be 

 of the highest optical and mechanical perfec- 

 tion, and reflect great credit upon Professor 

 Eitchey, its designer, and those who have been 

 associated with him in the extensive work of 

 construction and erection. Photographs of 

 nebulae made by Professor Eitchey, and a 

 series of photographs of the great nebula in 

 Orion, made through a red screen by the 

 writer, are of exquisite sharpness and perfec- 

 tion of detail. The star images are extremely 

 small, and the wealth of faint stars shown 

 leaves no doubt that in light-grasping power, 

 as well as in optical resolution, the telescope 

 will meet our highest expectations. One of 

 the most gratifying results of these tests is the 

 proof they afford of the excellence of the night 

 conditions on Mount Wilson. Por the last 

 four consecutive nights (January 16, lY, 18, 

 19) the definition with the full aperture of 

 60 inches has been essentially perfect from a 

 photographic standpoint. This is in the midst 

 of the rainy season, when the atmosphere is 

 far less steady than during the unbroken suc- 

 cession of clear days and nights of summer. 

 A telescope of 100 inches aperture, or even 

 larger, could certainly be used here to great 

 advantage on nights such as we have already 

 tested. Fortunately, Mr. John D. Hooker, of 

 Los Angeles, has agreed to meet the expense 

 image is required. The 60-inch and 100-inch 

 reflecting telescopes, of great aperture and smaller 

 focal length, are not suitable for solar observa- 

 tions, but will be used for the study of stars and 

 nebulse. 



