10 
MESSES. DE LA EUE, STEWART, AND LOEWY’S EESEAECHES 
-A. — ^ = — f— 45 35-3 
¥=- 4-4 
(^-90°)l. to III. =—43 22-2 
+ 2 8-7 
Fig. 5. 
10 h 37 m . 
1. 
2. 
3. 
4. 
5. 
p. 
0-297 
1-716 
0-894 
1 22 7-7 
124 9-3 
Q. 
0-320 
1-693 
0-882 
297 21*3 
299 22-9 
R. 
1-764 
0-249 
0-130 
353 54-0 
355 55-6 
S. 
1-080 
0-933 
0-486 
322 14-7 
324 16-3 
s. 
1-129 
0-884 
0-461 
330 37-5 
332 39-1 
ll h 14 m . 
P. 
0-308 
1-704 
0-889 
121 
56-5 
124 
5-2 
Q. 
0-319 
1-693 
0-883 
297 
15-3 
299 
24-0 
R. 
1-760 
0-252 
0-131 
353 
18-3 
355 
27-0 
S. 
1-077 
0-935 
0-488 
322 
5-8 
324 
14-5 
s. 
1-129 
0-883 
0-461 
300 
32-3 
302 
41-0 
10. We pass now to the second part of the reduction of the measurements, viz. the 
calculation of the heliographical positions derived by knowing the observed distance of 
a spot from the centre of the sun and also its angle of position. 
This part of the work may be conveniently divided into the following successive stages. 
As already mentioned, we have here entirely followed the method of Mr. Carrington, who 
by introducing tabulated auxiliary values has condensed the two steps necessary for 
passing from the ecliptical longitude and latitude to the heliographical into one. 
First, if r denote the measured distance of a spot from the centre, Fig. 6. 
R the measured radius of the photogram, and (R) the tabular semi- 
diameter of the sun in minutes of arc ; then, in order to express our 
measured distance in terms of the tabular radius, which required 
value we may call we have the proportion 
r : §' : : R : (R) 
H* -W ( 1 ) 
Now it will readily be seen from fig. 6 that O' S' is larger than O S, 
or that the measured distance requires a correction to deduce from 
o s 
it the value Qfg for finding the true angular distance of a spot from 
