Mr, Atwood’s Theory for the Men juration 
the angle of incidence on the fixed fpeeulum j the correfponding reparation of 
'fX*/ I — ViP x i — p~ 
the images will be — : 
V i 
- nt 
’ + nrp 1 
.(p. 429,) which is the greateft poffible 
w 
hen p — 
tom 2 + nft — 3 
4 m 
— fine of 35° 1 47" (if 
m 
iin. 
7 ♦ 
c 
nnd j“ fin* 1 o', as in tab. I. and II.) being thenar — — 5 but if rrirfin. 30", as in 
1 b 37 
£ 
tab. III. the greatqft reparation will be only — — * correfponding to lefs than one- 
3074° 
third of a degree for the images motion through 10' in the field of the telefcope. 
In like manner let a line be drawn through the center of the field perpendicular to the 
line before deferibed; any deviation of the points in contact through a frnail angle 
/in the direction of this line will caufe the plane of reflexion at the fixed fpeeulum 
to be inclined to the primitive fecondary with which it fhould coincide at an 'angle rS 
\mp 2 se x Vi - j 2 X ^ t -p 1 
- : this will occafion a reparation of the images = — 1 
m v i-M + m p 
(page 429. — being there fubftituted for d) which is the greateft poffible when 
4 
t/g— 8;?z ^ 3 4 7)1 ^ j£ m p n> ^ a qd s rr fin. 10'* as in tab. I. and II. 
d 
the greateft feparation of the images will be ™ ^ : but if s — fin. 30 
e • 
and * = fin. f, as in tab. III. it will only = ~ " hich anfwerS t0 
a divarication of lefs than 1"' for the images motion through 10' in the field 
of the telcfcope, in the diredion of the line above deferibed, which is drawn 
■through the center of the field, and perpendicular to the fixed plane of refledion. 
It rauft be remembered, that the Reparations of the images here eftimated are 
greater than can poffibly happen in thefe conftrudions, when the index is 
direded to any other points of the circumference of the plane of motion (the 
di fiance of the images from the center 'the field not exceeding 10 ) and are, 
t‘ven in this cafe, phyfically fpeaking, evanefeent. 
T A B L 
