52 



O. A. Åkesson 



What is chiefly of interest to us in this connection is the fact that, while the 

 excess is thoroughly positive in the motions we have investigated, no such positive 

 excess exists in the material of Dyson and Maundkr. The main difference between 

 this material and that of the author consists in the latitude motions of the former 

 being computed from an interval of one day. How is the difference between the distri- 

 butions of the motions then to be explained? One might possibly think that the 

 positive excess inay have arisen in the following way. Suppose the currents in the 

 solar atmosphere to have an arbitrary velocity, and further suppose that these 

 velocities form a normal distribution. Thus, if the spots moved with the same 

 velocity as these currents, the distribution of the motions of the spots would also 

 be normal. However, it now seems very plausible that the velocities of the currents 

 are not immediately reached. There should evidently arise a certain accelei-ation in 



4 —3 -2 —1 0 +1 +2 +3 +4 



Fig. 6. Proper Motion in Latitude of Recurrent Spot Groups compared with a normal Distribution. 



the motions of the spots till the velocities of tlie spots become approximately as 

 jarge as that of the currents. Now, if the velocities are determined from shorter 

 intervals, there is a possibility of a greater number of small velocities being obtained 

 than those corresponding to the normal distribution. 



Too great importance, however, should not be attached to this attempt to 

 explain the positive excess. The actual cause of the excess must rather be regarded 

 as still uncertain. 



B. On the Position of the Sun's Axis. 



In the introduction, page 8, I mentioned some of the more important determi- 

 nations of the rotation axis of the sun. The heliographie co-ordinates of the spots 

 published in the Greenwich Observations are calculated by employing Carring- 

 ton's values: /— 7''lô'; L = TS^iC. In using the observations of 867 recurrent spots 



