510 
EARL ROSSE’S OBSERVATIONS ON THE NEBULJ5. 
l-incb focus; a great number of stars clearly visible in it, still Herschel’s rings not 
apparent, at least no sueh uniformity as he represents in his drawing. 
April 11, 1844. — Observed with the 3-feet instrument, two friends assisting; both 
saw centre clearly resolved. 
April 26, 1848. — 6-feet instrument. Saw the spirality of the principal nucleus 
very plainly ; saw also spiral arrangement in the smaller nucleus. 
The following measurements were taken by my assistant, Mr. Johnstone Stoney, in 
the spring of 1849 and 1850. 
Mean of the 
observations of 
position. 
No. of observa- 
tions. 
Greatest diifer- 
ence between 
observations and 
the mean. 
Mean of the 
observations of 
distance. 
No. of observa- 
tions. 
Greatest differ- 
ence between 
observations and 
the mean. 
o / 
O / 
/ it 
// 
N. n. 
16 34 
4 
3 27 
4 22’2 
4 
9-6 
N. 1. 
52 4 
1 
2 6-6 
1 
N. 2. 
54 0 
4 
1 57 
5 0-0 
4 
5-4 
N. 3. 
104 20 
2 
2 3 
2 45*6 
2 
3-6 
N. 4. 
111 57 
2 
0 40 
4 3-6 
2 
0-6 
N. 5. 
165 35 
2 
0 31 
1 43-2 
2 
1-1 
N. 6. 
191 42 
1 
3 54-0 
1 
N. 7. 
211 2 
1 
2 36-6 
1 
7, 8. 
270 42 
1 
0 34-8 
1 
N. 9. 
231 32 
4 
3 35 
1 23-4 
3 
6*6 
9, 10. 
197 57 
1 
0 27-0 
1 
N. 11. 
279 21 
4 
4 18 
1 49-8 
3 
22-2 
11, 12. 
225 27 
1 
0 12-6 
1 
N. 13. 
281 37 
2 
0 22 
3 59-0 
1 
14, 
15. 
297 15 
1 
N. 15. 
310 34 
4 
4 17 
2 55-8 
4 
13-8 
N. 
fS 22-8 
2 
0-1 
N. /3 
5 7 
• « • 
1 28*2 
3 
3-0 
N. y^ 
1 
2 37-8 
3 
2*4 
N. n 
ri 46-2 
1 
N. £ 
2 46-8 
1 
N. ? 
" 
9o 7 
... 
i 
1 40-8 
1 
N. 
3 15-6 
1 
Observations. — There is a great discrepancy between the measured position of 11 
and 12 and the rough diagram made at the time of observation. 
N. 13 is twice noticed in the observing-book. 
Once N. 11 , 13 is taken as one position; the other times N. 11 and 13 are taken 
separately, N. 13 being made 1° 40' less than N. 11 ; hence 2/0° 31' is a more pro- 
bable position for N. 13 than that given in the Table. 
The Greek letters are perpendiculars from N. on tangents to the outsides of the 
convolutions, the tangents from a, (3, y being vertical, that is, parallel to the position 
95° 7'j and those for h, s, horizontal, i. e. parallel to position 5° 7’- 
The greater part of the observations were made when the eye was affected by lamp- 
light, which made it difficult to estimate correctly the centre of the nucleus ; it was 
of importance that no time should be unnecessarily spent, and after the lamp had 
been used a new measure was taken, as it was judged that the object was sufficiently 
seen. With the brighter stars this would frequently happen before the nucleus was 
