452 _ E. S. Holden—Proper Motion of the Trifid Nebula M. 20. 
With reference to the distribution of the  , in 
Mason’s figure we may lay down the following propositions 
A. The brightest nebulosity is that immediately following 1, 
19; that surrounding his star 5 [= Lassell No. 18], and that near 
; Mason 6. 
The fainter orders of nebulosity are pretty uniformly and 
C, ET acuta disposed about these three brighter centers. 
This is better understood from the figure than from a description. 
D. Stars 12 and 13 are immersed in nebulosity. 
E. Star 11 follows the edge of the nebula a considerable distance. 
Star 6 is somewhat immersed in 
H. Star 5 is on the preceding edge of 
J. triangle whose vertices would ‘be in the positions of 
Lassell’s stars 40, 44, 21 is completely filled with tolerably bright 
nebulosity. 
. The stars Mason 6 and 4 are both immersed in nebaloelty,® 
in very faint nebulosity, 4 in a brighter part. The chan 
is south of these. The 40 of 6 and 4 is according to Maton 
—63" and —39", 
L. The 46 of the south edge of B is-about the mean of the 46’s 
of stars [Mason] 4 and 6, that is, about 51”. About 7° pease: 
1, the 4o of the aeesae "northern limit nt C is about 18 
In regard = i distribution of the nebulosity in Lassell’s 
figure we may remark : 
A. ca sick nebulosity is immediately about and following 
wh 2, 
B. The next order of bright ‘aoa = about stars 35, 36, 37; 
i. €., just south of 1, 2, 19 in the lin 
C. The third order of bright cenaac aia is between stars 12, 48, 
40 and stars 40, 18. 
tars 12, 13, 52 and 53 are immersed in nebulosity. 
E. Star 11 is just on the edge of A. 
F. Star 26 is just on the edge of A. 
G. Star 6 is nearly in the middle of the dark channel y. 
H. Stars 5, 27, 28 are immersed in the following border of B. 
J. The triangle 40, 44, 21 is tree of nebula. 
K. The pit gH 36, 35 are immersed in C south of the channel a. 
LL. The southern limit of B instead of iia as in Herschel and 
Mason’s hited 4 ver 100” south of 1, is over 60” north of it. 
The 46 of the north shore of C is tedghity) about — 70”, 
Lassell’s ne figure confirms the above propositions in gen- 
eral. The only changes necessary to introduce are with 
regard to— 
D. 12, 18, 52 on the edge or following the edge of B. 
F. Star 26 outside of A. 
H. 5, 27, 28 follow the east edge of B. 
. The triangle has a patch of faint nebulosity in it (4’). 
