E. S. Holden—Proper Motion of the Trifid Nebula M. 20. 447 
Position of the mass A relative to the triple star. 
Ir will be convenient to examine the various drawings with 
regard to ak situ! and to lay down a series of bom 
e com- 
original ones and the propositions I have derived from 
them. In the actual examination of the drawings, each one 
was studied separately, and all the evidence to be derived from 
it recor nd the various data were subsequently collated. 
In this way a é tolerably pnt judgment can be formed. 
In Sir John Herschel’s Cape of Good Hope figure we find: 
I. Stars 1-2-19 are on the very edge of A. 
II. The line 12-13 does not pile a t A, 
Ill. The star 20 is not laid 
IV. The line 1-10 is not rales le precedin 
V. The star 35 is not laid down on = caving although 
given in the Catalogue 
In general the soreenient with Mason’s drawing is good for 
‘ e mass A near 1, 2,19. In the figure given by Mason and 
mith : 
I. Stars 1-2-19 immersed in 
II. The me 12-13 does not pees A, but passes west of it 
by about 1 
II. The . star 20 is not laid down, as it was too faint for Mason’s 
bee = 
e line 1-10 preceding 1 is involved in A by a little over 
14”. 
V. 35 is not laid down in his drawing. 
These measures are not made on the engraving representing 
the nebula as it appears to the eye, but on the contour map 
(Mason's Plate II). The two plates agree however, but the 
second is more useful for a purpose like the present one, as it 
was seen by Mason that it would be. 
ring his residence at Malta in 1862-4, Lassell presented 
to the Royal Astronomical iety a figure “ei this nebula 
drawn under his coerne which is referred to in the Memoirs 
that work. This Seater bed not be here given, as essentially 
the same observations are represented in Lassell’s second 
