206 CARNEGIE INSTITUTION OF WASHINGTON. 



find that it corresponds with that of the earth, i. e., the north mag- 

 netic pole Hes near the north pole of rotation.* While this analogy 

 may prove to be important in the further consideration of various 

 theories of the earth's magnetism, there is one respect in which the 

 sun's field may differ very materially from that of the earth. As 

 various solar lines exhibiting large Zeeman effects in the laboratory 

 have failed to give any indication of the sun's field, and as the great 

 majority of the lines which show displacements are produced at low 

 levels in the sun's atmosphere, it seems probable that the intensity 

 of the field must fall off very rapidly in passing upward from the sur- 

 face of the photosphere. This point will be the subject of a careful 

 inve >tigation as soon as the necessary material becomes available. 



A determination of the exact position of the magnetic poles with 

 respect to the poles of rotation will be made as soon as suitable 

 observational data can be obtained. 



Professor Koch's registering micro-photometer is being tested in the 

 measurement of the displacements on general magnetic field spectra. 

 The results, as far as they go, confirm those obtained with the parallel 

 plate micrometer, but definitive work must await the construction of 

 an instrument giving more accurate relative motion of the negative 

 and the plate on which the curve is photographed. 



Soon after it appeared that the displacements observed in the above 

 investigation were reasonably attributable to the Zeeman effect, 

 Dr. Anderson was requested to calculate the displacements of a 

 normal Zeeman triplet at various latitudes, assuming the source to be 

 in the field of a uniformly magnetized sphere. The resulting sine 

 curve was later the subject of a valuable theoretical study by Mr. 

 Scares, which has supplied the formulae required for the reduction 

 of the measures. For a normal triplet the theoretical displace- 

 ment curve is a function of the heliographic latitude, the position 

 of the observer, and the solar magnetic elements. As already 

 stated, it is a sine curve having zero values near the equator and the 

 poles and absolute maxima near 45° north and south latitudes. Mr. 

 Seares's theoretical investigation included the effect of the elliptical 

 polarization produced by the mirrors of the tower telescope, which are 

 found, under the actual conditions of observation, to flatten the curve 

 of displacement by a negligible amount. 



Spectrum of the Chromosphere. 



Miss Burwell has measured 12 photographs of the spectrum of the 

 chromosphere during the year, but unfavorable weather and the con- 

 stant need of the 150-foot tower telescope for observations of the 



*The nomenclature ordinarily used by terrestrial magneticians is followed here. As 

 a matter of fact, the magnetic poles in the northern hemispheres of the sun and earth are 

 "south" poles. 



