ASTRONOMY: PEASE AND SHAPLEY 
99 
evident. To overcome the small or accidental groupings of the stars 
it appears necessary to have several hundred in each sector. No import- 
ant systematic differences between diametrically situated sectors ap- 
pear in figure 2, and, to eliminate possible errors of centering, the mean 
of the numbers for opposite sectors may be combined in discussing the 
results. 
TABLE I 
Ellipticity for Different Exposures and Magnitude Intervals in Messier 13 
PLATE NO. 
DtJRATION 
OF EX- 
POSXIRE 
TOTAL 
NO. OF 
STARS 
NUMBER OF STARS IN SECTORS 
A 
B 
c 
D 
E 
F 
G 
H 
I 
J 
K 
L 
13 
6m 
5,800 
211 
149 
163 
198 
235 
256 
174 
154 
154 
213 
214 
235 
14 
15 
7,700 
433 
264 
296 
305 
309 
401 
259 
230 
284 
314 
420 
396 
19 
22 
14,150 
744 
672 
734 
738 
852 
825 
684 
583 
569 
638 
814 
859 
15 
37.5 
16,600 
913 
770 
749 
763 
963 
1011 
974 
804 
779 
853 
1026 
1008 
16 
94 
25,000 
1475 
1340 
1261 
1361 
1580 
1590 
1486 
1343 
1338 
1431 
1580 
1590 
133 
300 
30,000 
1254 
1234 
1126 
1258 
1368 
1300 
1187 
1085 
1079 
1232 
1463 
1416 
15 minus 13 
702 
621 
586 
565 
728 
755 
800 
650 
625 
640 
812 
773 
16 minus 15 
562 
570 
512 
598 
617 
579 
512 
539 
559 
578 
554 
582 
TABLE II 
Ellipticity and Distance from Center in Messier 13 
PLATE NO. 
DISTANCE FROM 
CENTER 
NIjMBER of STARS IN SECTORS 
A 
B 
C 
D 
E 
F 
G 
H 
I 
J 
K 
L 
16 
2' to 4' 
750 
668 
623 
670 
718 
778 
758 
683 
712 
728 
764 
762 
4 to 6 
423 
361 
358 
394 
479 
438 
402 
352 
330 
386 
476 
464 
6 to 8 
212 
207 
168 
198 
249 
248 
214 
194 
188 
202 
226 
236 
8 to 10 
90 
104 
112 
99 
134 
126 
112 
114 
108 
115 
114 
128 
133 
3 to 5 
624 
640 
560 
662 
712 
658 
629 
597 
586 
642 
788 
684 
5 to 7 
410 
374 
362 
394 
424 
396 
358 
292 
302 
360 
431 
471 
7 to 9 
220 
220 
204 
202 
232 
246 
200 
196 
191 
230 
244 
261 
9 to 11 
116 
136 
141 
100 
134 
157 
130 
124 
131 
129 
130 
118 
The relation of the ellipticity to brightness is also shown in Table I. 
Thus Plate 13 includes stars between photographic magnitudes 13 and 
17.3; the next to last row of the table refers to the interval 17.3 to 19, 
and the last row to the interval 19 to 20. The magnitudes depend 
mostly on extrapolations and are subject to some uncertainty. 
The plates of long exposure, Nos. 16 and 133, show a sufficient num- 
ber of stars in each sector to permit a subdivision with respect to dis- 
tance, the results of which are in Table II. Because of the relatively 
small number of stars, accidental deviations greatly mask whatever 
ellipticity exists in the outer ring. The counts of stars within distance 
2' on the plates of shorter exposure also show the elliptical form, and 
give the same general orientation. 
