ANALYSIS OF SOLAR RECORDS 77 



tism. Disturbances are estimated on a scale of to 2 and averages made of 

 many stations so that the data may represent widely distributed terrestrial 

 conditions. It is accepted that this phenomenon is due to the sun and yet 

 the exact machinery by which these effects reach the earth's magnetism is 

 not certain. It is probable that streams of charged particles come from the 

 sun from active areas near the solar meridian, but it is also thought possible 

 that there is an effect from short-wave radiation in the form of ultra-violet 

 light. Motion of our upper atmosphere may carry electric charges received 

 from the sun or developed from solar radiation in such a manner that magnetic 

 fields are produced. There is close connection between terrestrial magnetic 

 disturbances and northern lights, earth currents and the so-called magnetic 

 storms that affect telegraph lines. 



Magnetic observations extend back to 1906 and in less accurate form to 

 1872 and in crude form to 1835, and constitute one of the longest sets of pre- 

 cise observations connected with the sun. In some respects, therefore, these 

 data rank very high as source material in any study of periodic values in solar 

 activity and must be included in our list. At the same time they illustrate 

 certain features of cyclogram analysis and open the way to further studies of 

 the sun and its phenomena. 



Observers who have made careful studies of periodicities in magnetic 

 data, state that the correlation of magnetic disturbances with sunspot 

 values seems to be low in short time intervals such as the day and the month, 

 but greatly improves as short variations are smoothed out and long intervals 

 (for example, the year) are considered. On the other hand, greatly agitated 

 days (magnetic storms) sometimes come when a large sunspot or group of 

 sunspots is central on the sun. Well-defined periods of about 27 days have 

 been found in the magnetic character figure C. Numerous coincidences with 

 known rotation values lead scientists to accept these periods as measures of 

 solar rotation. There is also in magnetic data a 6-months cycle that can be 

 traced back to 1872. A very minute effect has been isolated, depending on 

 the lunar day (Chapman: 1918). 



Solar Rotations in Magnetic Data — One of the productive methods hitherto 

 employed in analyzing the magnetic data is Dr. Bartels' graphic solution in a 

 multiple plot (1932; see Chree and Stagg in Bibliography; for multiple plot 

 see Chapter II) giving daily values arranged in rows as if in a summation 

 process. In this pattern his eye has caught discontinuous periods as men- 

 tioned above under that topic. Thus he has confirmed the semi-permanence 

 of the magnetic source areas or M-regions in solar longitudes and at the same 

 time has found some evidence of activity in opposite longitudes of the 

 sun. His later application of probability principles produced his theory of 

 "quasi-persistence." He treats this phenomenon as a general character 

 rather than as a phenomenon localized in time, and yet his summation dial 

 enables him to date some cyclical changes. 



In 1935, desiring to compare cyclogram analysis with Bartels' summation 

 dial of magnetic data in which he investigated "quasi-persistence" (fig. 26) we 



