12 



O. A. Åkesson 



and that of drift II by 



4 = 140.69 — 20.65 siirß. 



The mean ratio of the number of sun-spots in maximum II to those in maximum 

 I is 1:2. — — — I do not claim that the conclusion I have arrived at, should 

 do more than approximate to quantitive precision.» 



Hitherto we have principally given an account of the motions in longitude. 

 Concerning the latitude-motions of the spots, it seems still to be uncertain whether 

 systematic motions do exist. Carkington's assumption of two streams directed 

 towards the poles and the equator does not seem to have been contirmed by later 

 investigations. Turner has, in some papers, dealt with the problem of the latitude-drift 

 of the sun-spots, in connection with a more accurate determination of the rotation- 

 axis of the sun. It is easily seen that an apparent latitude-drift with a period of 

 one year may be explained by the assumption of a wrong determination of this 

 axis. From the researches of Turner, no conclusion can be drawn as to whether 

 a real latitude- drift exists, or whether the axis of the sun needs a correction. 

 Another alternative is that the sun's equator might be subject to a precessional 

 motion, though this seems very improbable, the sun not being visibly flattened. 



Dyson and Maünder ^ have recently carefully examined the question of the 

 position of the rotation-axis. They call attention to the fact that changes in the 

 apparent latitude of a spot-group may arise from three causes: 



l:o. An error in the assumed position of the sun's axis (Carrington's values 

 7= 7» 15'; L = 73040'. 1850.0). 



2:0. An actual motion of the spot on the sun's surface. 



3:0. Errors of observations or of measurement; particularly such as would 

 introduce error in the determinations of the photographs. 

 To these three causes one might also add the influence of the refraction in the 

 solar atmosphere. 



Should an error occur in the position of the assumed rotation-axis, it would 

 cause an apjmrent drift in the latitude-motions of the spots, even if there existed no 

 actual drifts. Dyson and Maunder, however, in their researches have not found 

 such a period of one year in the motions of the spots. But taking into considera- 

 tion the great mean errors in the averages, that is not so strange. As the result of 

 this investigation the authors get 



å/= — 4'.4; 

 ALsin 1= + 1'.7. 



Here A/ designates the correction of the assumed inclination 7, and the correction 

 of the longitude of the ascending node of the sun's equator. Regarding the actual 



^ F. W. Dyson and E. W. Maunder: The position of tlie sun's axis as determined from 

 Photograplis of the sun from 1874—1911, measured at tlie Royal Observatory, Greenwich. Monthly 

 Notices, May 1912. 



