458 ES. Holden—Proper Motion of the Trifid Nebula M. 20. 
misinterpretations are likely to occur. It is for this reason 
that I have given my own observations in detail, so that they 
may be repeated step by step at any subsequent time; and for 
the same reason, I have given in full the analysis of the sepa- 
rate drawings so that each point can be verified or rejected by 
any one who has the original drawings before him. 
This method of examining each drawing, deducing from it 
all the evidence on all the points in question, and then collating 
the various data under each separate head, not only enables the 
whole work to be quickly verified, but it enables the person 
collating the evidence to form the final conclusions with little 
or no danger of bias or prejudice. The principal question is as 
to the goodness of the evidence itself. It may be worth while 
in this case to examine the evidence and to see what must be 
rejected in order to suppose that this nebula has remained wn- 
changed from 1784 to L877. First then, Sir William Herschel 
speaks of the triple star as being ‘in the middle” of the three 
nebulosities on several occasions. Sir John Herschel is explicit 
as to its being “in the midst” and “exactly in the center” of 
the “central vacuity.” Inference A rests on these statements, 
which could not have been made more definite by Sir John 
Herschel and which are strongly corroborated by Sir William - 
Herschel. 8 is undoubtedly correct. Heénce I believe that 
the previous inferences regarding the relative motion of t 
triple star and the nebula should stand, and are correct. 
e further conclusions as to change, as I have given them, 
could have been deduced from the drawings of Mason and 
to be solved, and his results are entirely trustworthy. In 
every point noted as “certain,” (and only such points are 
aracter. In regard to my own obser- 
vations, I am satisfied that they are, in the main and on essential 
points, correct. The season of 1877 was very unfavorable and 
the star positions could be improved, but I do not think any 
error of moment remains. It therefore seems to me that the 
evidence remaining to be examined is such that it ought not to 
be rejected, and that the previous conclusions should stand. 
