[PLASKETT-DELURY] THE SOLAR ROTATION 31 
(c’) Obtain the ratio of V, to V, from the formula of Adams, or 
more simply from the curve representing the change of linear velocity 
with latitude. 
(d’) The final velocities V, and V, can then be obtained from the 
formula 
V, cos 7, + V, cos 7, = 2(v + oe s) 
R 
It may be seen by comparing the residuals in Table IX, Section 19, 
that they are practically the same for the three reduced values of each 
observed value obtained by the two methods of reduction, and it is 
therefore immaterial so far as accuracy is concerned which is employed. 
Both have been carried through in this investigation for the sake of 
comparison and to determine which is the more suitable. 
SUMMARY OF MEASURES. 
13. It is impossible within the limits of this paper to give the 
separate measures for each spectrum, and so in the succeeding tables a 
summary of the measures and other necessary data are given. In 
series I the 19 lines given in the preceding tables were measured on 14 
of the 19 plates. On the remaining 5 plates, 8 of the best defined lines 
only were measured. This number was reduced to diminish the great 
labor of measurement and because the measures of the 14 plates had 
shown that, as will be seen later, any differences in rotational value 
for different elements were accidental in character. Furthermore, 
even with the reduced number of lines, the probable error of a plate 
as determined from the internal agreement among the lines was on 
the average less than half the probable error obtained from the measures 
of different plates. In series IT, however, owing to the much higher 
probable error of measurement all the lines were measured throughout 
and in series ITI also on account of the systematic differences previously 
found for the different lines by Adams. 
In these summaries @, g, and V, V, represent as above the latitudes 
and velocities at the observed points on the dise of the sun, while g and 
V are the latitudes and velocities at the points radially projected 
through the observed points to the limb. 
