E. 8. Holden— Proper Motion of the Trifid Nebula M. 20. 457 
RECAPITULATION OF THE PRECEDING RESULTS. 
We may now collect such of the Plena results as we have 
found bigelibat de First it has appeare 
. H 1784, July 12 to 1833, the triple star was centrally 
situated ranean g oe three sobulosiiioe 
Again, 
%. From 1839 to 1877 the triple star was not centrally situated 
between the three nebulosities, but involved in A.. 
It has previously been seen that each of these Rope 
rests on a firm basis. Granted that A and 8 are correct, I 
know of but three ways to reconcile the opposing face: ; 
a, The triple star une a large Propet s motive 
6. The nebula A has a large proper 
ce. The nebula A is s subject to derided changes of gear 
T 
in progress. The relative positions of 1 and the various stars 
a 
as is probable, the proper motion of the triple star fs si: 
We have seen that the evidence with regard to the pbeitidik 
of the nebulosity A relative to the star 6, indicates changes in 
the brightness and position of this part o his appears to 
be connected with changes much less certain near star 5, ete. 
It has also pants that in 1839 the nebula B was about the 
stars Mason 4 and 6. This is confirmed by Herschel’s earlier 
Each of the above inferences rests on undoubted authority, and 
only cases are included here in which no doubtful points have 
arisen. It therefore appears to me to be a just conclusion that— 
he evidence as recorded with regard to this nebula indicates 
marked changes of position or brillianey, or both, during the 
period 1784-1877. The conjecture of Sir John Herschel, “perhaps 
this ost Sea object has a proper motion,” will be recalled i in this 
connectio 
I have, s my own mind, no doubt but that the evidence as 
recorded, if Nicer pele he. by any competent person will 
o the same conclusion. The examination of many draw- 
ings of nebulz has, however, led me in common with others, 
to the conclusion that too great care cannot be exercised in 
Drawings and observa- 
tions made from one point of view have to be interpreted 
from quite another and a different one, and misreadings and 
es 
4 
@ 
bas 3 
Tc 
® 
a. 
B 
a 
2 
s 
a 
% 
as 
er 
5.09 
a 
2 
=) 
Ra 
wa 
