92 SCHULTZ-STEINHEIL, ON THE ELEMENTS OF THE SUN's ROTATION. 



The result of tliis examination of Duner's observations of 

 the sun is thus that tlie sun rotates with uniform velocity 

 round an axis the inclination of which towards the axis of the 

 ecliptic is 18M2, the longitude of the intersection of the sun's 

 equator with the ecliptic being + 28°. 00. It will be of great 

 interest to examine whether further spectroscopical observations 

 of the sun made during all seasons will agree with that; if so, 

 I think it is proved that the sun's rotation is uniform. It is 

 no easy matter to bring this in accord with the experiences 

 found from observations of the sunspots; perhaps it will become 

 possible to explain this anomaly by assuming proper motions to 

 the spots. It had been my intention also to reduce the observa- 

 tions of Crew, but infortunately I have not all necessary 

 dates. 



There are several circumstances that may make this deter- 

 mination rather doubtful, viz. the uncertainty as to which quad- 

 rant the observations in group 7t = 90° were made, which do 

 not at all events very much influence the result; another cause 

 of error is the foUowing: Duner says pag. 73: »Pour les ob- 

 servations dans le voisinage des pÖles, on pourrait au contraire 

 suspecter qu'il y a eu, dans les observations, confusions des bords 

 solaires, de la sorte que des observations qui devaient étre prises 

 sur le bord est se sont en efFet portées sur le bord ouest ou 

 vice versa, erreur qui ne se trahit pas par l'apparence seule du 

 groupe des raies mesurées que quand on observe dans une lati- 

 tude de 45° et dessous. Mais bien qu'il est fort possible, que 

 des erreurs de cette espéce puissent arrivé, j'ai cru, cependant, 

 qu'il vaudrait mieux ne pas faire des suppressions ou alterations 

 arbitraires des observations etc.» Faults of that sort especially 

 afFecting the highest latitudes would of course considerably in- 

 fluence the result by producing great changes in the values of i 

 and jQ. 



Another source of error may occur if the observations are 

 not corrected for the earth's motion round its axis. Thus an 

 observation on the east limb of the sun gives a value of v less 



