454 FE. 8. Holden—Proper Motion of the Prifid Nebula M. 20. 
It is possible that the brightness of the stars 1, 2, 19 pro- 
duces ss contrast part of the effect noted. 
spite of minor nyt ta the general agreement as to the 
seustion “Ot stars 12 and 13 is good. Lassell’s first drawing if not 
corrected by his second would be difficult to explain im this 
ect. 
3 According to Herschel: star 11 is immersed in A; Mason, 
star 11 is dee eply i immersed in A; Lassell, star 11 is just on the 
edge of A; Langley, star ab is not immersed in A; Trouvelot, 
star 11 is very slightly immersed in A; Holden, star "11 is on the 
bie Ms edge of the br am Fa eiesitiy, but follows the extreme edge 
a 
Here Herschel aa Mason agree with each other, but differ 
from the later authorities. 
F. According . Lassell: star 26 is just on the edge of A; that 
is, the space between 26 and 5 is totally black. In his first fig- 
star 26 is within the brighter medley of A, whose boahdary 
ine runs between 5 and 26 at a distance from 26 equal to about 
4 the distance of these stars. 
The evidence under this head should be considered in con- 
nection with that under H, which is for comparison next given. 
H. According to Herschel: star 5 is on the Wee edge of 
_A; Mason, star 5 is on the preceding edge of A; Lassell, stars 
5, 27, 28 are immersed in the following border of B. In Lassell’s 
first figure these three stars are entirely free from nebulosity and 
follow the east edge of B; Langley, star 5 “e shots mae Pe 
velot, star 5 is weiter A; Holden, stars 5, 2 € on 
veding edge of a fainter strip of nebulosity which bepiite ae yt to 
horder A and continues northward beyond 28. The preceding 
edge of the brightest parts of is is very close to 11, a little east 
18 b 
been able to see how the exact effect given in Lassell’s two draw- 
ings (by two different observers, be it remembered, at different 
times) can be produced. At the’ same time, I have no doubt that 
the appearance given by Lassell was a true one for 1862-4, and a 
slight change in the intensity of the nebulosity between 26 and 5 
would reduce the nebula as — in the Ww 
mo to the appearance’as given by Lassell. A change in the 
verse direction is-needed to shoes, 3 the appearances given by 
treecil and Mason 
