. Popular science monthly. Fig. 13. 150-foot Toweb Telescope. as to the proportion at different levels of positive and negative elec-trons, and of the perturbations due to currents in the solar atmosphere,must delay the most effective application of these methods, though theypromise much future knowledge of the magnetic field at high levels inthe solar atmosphere. Of the field at low levels, however, they may tell us little or nothing,for the distribution of the electrons may easily be such as to give riseto a field caused by the rotation of the solar atmosphere, which mayoppose in sign the fi
. Popular science monthly. Fig. 13. 150-foot Toweb Telescope. as to the proportion at different levels of positive and negative elec-trons, and of the perturbations due to currents in the solar atmosphere,must delay the most effective application of these methods, though theypromise much future knowledge of the magnetic field at high levels inthe solar atmosphere. Of the field at low levels, however, they may tell us little or nothing,for the distribution of the electrons may easily be such as to give riseto a field caused by the rotation of the solar atmosphere, which mayoppose in sign the field due to the rotation of the body of the detect this latter field, the magnetic field of the sun as distinguishedfrom that of the suns atmosphere, we must resort to the methodemploAed in the case of sun-spots—the study of the Zeeman effect. If 120 THE POPULAR SCIENCE MONTHLY. Pig. 14. Head of the 75-foot Spectrograph of the 150-foot Tower Telescope. this is successful, it will not only show beyond doubt whether the sunis a magnet: it will also permit the polarity of the sun to be comparedwith that of the earth, give a measure of the strength of the field atdifferent latitudes, and indicate the sign of the charge that a rotatingsphere must possess if it is to produce a similar field. I first endeavored to apply this test with the 60-foot tower telescopein 1908, but the results were too uncertain to command confidence. Thanks to additional appropriations from the Carnegie Institutionof Washington, a new and powerful instrument was available on MountWilson for a continuation of the investigation in January, 1912. Thenew tower telescope has a focal length of 150 feet (Fig. 13). To preventvibration in the wind, the ccelostat, second mirror and object-glass arecarried by a skeleton tower, each vertical and diagonal member of whichis enclosed within the correspon
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