56 THE ROYAL SOCIETY OF CANADA 
what has been found by comparison of the measures. Moreover, this 
difference, when the necessary allowance is made for the difference 
of the co-efficients of the second terms, is 0.044 km. or 0°.33 which is 
not far from the assumed 0.040 km. 
21. For convenience of comparison the previously obtained 
formule are tabulated beside those just given and we at once notice a 
remarkable similarity between the Ottawa and Mt. Wilson co-efficients. 
TaBLE X.—FORMULAE FOR SOLAR ROTATION. 





Observer. V, Linear Velocities. 5, Angular Velocities. 
Dimére hs: enh ap A ee ee AN EME eee 10°-60 + 4°-21 cos 
Étant ERA wae RE Sp be Cee Nay eee 12 -03 + 2 -50 cos 
Adams (1906-7)..... (1-575 + 0-480 cosv) cosy | 
Ae (OOS). (1-507 + 0-546 cos’g) cose | 10-57 + 4 -04 cos 
Adams (Mean).....  (1-550 + 0-501 cos’v) cose 11 -04 + 3 -50 cos’¢ 
Plaskett (1911).....| (1-483 + 0-532 cos) cose | 10 -32 + 4 -05 cos’ 
De Lury (1911)....| (1-448 + 0-523 cos) cose 10 -04 + 4 -00 cos 

This is especially the case with the 1908 Mt. Wilson determination 
and the mean formule from Series I and III where, in the angular 
form, the difference is only in the constant term. In the linear form 
also they are quite similar, and their agreement in both forms is so 
marked as compared with the widely different co-efficients obtained 
from the 1906-7 Mt. Wilson observations as to confirm the presence 
of some systematic error in the latter, suspected by Adams, and to 
indicate the substantial accuracy of the law of variation obtained. 
22. For convenience of comparison the daily angular value of 
the rotational velocity has been computed from the empirical formule 
given in the preceding table for the latitudes from the equator to the 
pole by intervals of 5°. A column containing the results of Storey 
and Wilson* at Edinburgh is added and a column for the velocities 
of sunspots, the means from three formule given in Adams’ f work. 
Further the linear velocities from Adams, 1908, and Plaskett’s formule 
have been computed and are given in the two last columns. 

* M. N. EXII, p: 674: 
+ Adams & Lasby, p. 118. 
